Spark-939: allow user jars to take precedence over spark jars

I still need to do a small bit of re-factoring [mostly the one Java file I'll switch it back to a Scala file and use it in both the close loaders], but comments on other things I should do would be great.

Author: Holden Karau <holden@pigscanfly.ca>

Closes #217 from holdenk/spark-939-allow-user-jars-to-take-precedence-over-spark-jars and squashes the following commits:

cf0cac9 [Holden Karau] Fix the executorclassloader
1955232 [Holden Karau] Fix long line in TestUtils
8f89965 [Holden Karau] Fix tests for new class name
7546549 [Holden Karau] CR feedback, merge some of the testutils methods down, rename the classloader
644719f [Holden Karau] User the class generator for the repl class loader tests too
f0b7114 [Holden Karau] Fix the core/src/test/scala/org/apache/spark/executor/ExecutorURLClassLoaderSuite.scala tests
204b199 [Holden Karau] Fix the generated classes
9f68f10 [Holden Karau] Start rewriting the ExecutorURLClassLoaderSuite to not use the hard coded classes
858aba2 [Holden Karau] Remove a bunch of test junk
261aaee [Holden Karau] simplify executorurlclassloader a bit
7a7bf5f [Holden Karau] CR feedback
d4ae848 [Holden Karau] rewrite component into scala
aa95083 [Holden Karau] CR feedback
7752594 [Holden Karau] re-add https comment
a0ef85a [Holden Karau] Fix style issues
125ea7f [Holden Karau] Easier to just remove those files, we don't need them
bb8d179 [Holden Karau] Fix issues with the repl class loader
241b03d [Holden Karau] fix my rat excludes
a343350 [Holden Karau] Update rat-excludes and remove a useless file
d90d217 [Holden Karau] Fix fall back with custom class loader and add a test for it
4919bf9 [Holden Karau] Fix parent calling class loader issue
8a67302 [Holden Karau] Test are good
9e2d236 [Holden Karau] It works comrade
691ee00 [Holden Karau] It works ish
dc4fe44 [Holden Karau] Does not depend on being in my home directory
47046ff [Holden Karau] Remove bad import'
22d83cb [Holden Karau] Add a test suite for the executor url class loader suite
7ef4628 [Holden Karau] Clean up
792d961 [Holden Karau] Almost works
16aecd1 [Holden Karau] Doesn't quite work
8d2241e [Holden Karau] Adda FakeClass for testing ClassLoader precedence options
648b559 [Holden Karau] Both class loaders compile. Now for testing
e1d9f71 [Holden Karau] One loader workers.
[SPARK-1390] Refactoring of matrices backed by RDDs

This is to refactor interfaces for matrices backed by RDDs. It would be better if we have a clear separation of local matrices and those backed by RDDs. Right now, we have

1. `org.apache.spark.mllib.linalg.SparseMatrix`, which is a wrapper over an RDD of matrix entries, i.e., coordinate list format.
2. `org.apache.spark.mllib.linalg.TallSkinnyDenseMatrix`, which is a wrapper over RDD[Array[Double]], i.e. row-oriented format.

We will see naming collision when we introduce local `SparseMatrix`, and the name `TallSkinnyDenseMatrix` is not exact if we switch to `RDD[Vector]` from `RDD[Array[Double]]`. It would be better to have "RDD" in the class name to suggest that operations may trigger jobs.

The proposed names are (all under `org.apache.spark.mllib.linalg.rdd`):

1. `RDDMatrix`: trait for matrices backed by one or more RDDs
2. `CoordinateRDDMatrix`: wrapper of `RDD[(Long, Long, Double)]`
3. `RowRDDMatrix`: wrapper of `RDD[Vector]` whose rows do not have special ordering
4. `IndexedRowRDDMatrix`: wrapper of `RDD[(Long, Vector)]` whose rows are associated with indices

The current code also introduces local matrices.

Author: Xiangrui Meng <meng@databricks.com>

Closes #296 from mengxr/mat and squashes the following commits:

24d8294 [Xiangrui Meng] fix for groupBy returning Iterable
bfc2b26 [Xiangrui Meng] merge master
8e4f1f5 [Xiangrui Meng] Merge branch 'master' into mat
0135193 [Xiangrui Meng] address Reza's comments
03cd7e1 [Xiangrui Meng] add pca/gram to IndexedRowMatrix add toBreeze to DistributedMatrix for test simplify tests
b177ff1 [Xiangrui Meng] address Matei's comments
be119fe [Xiangrui Meng] rename m/n to numRows/numCols for local matrix add tests for matrices
b881506 [Xiangrui Meng] rename SparkPCA/SVD to TallSkinnyPCA/SVD
e7d0d4a [Xiangrui Meng] move IndexedRDDMatrixRow to IndexedRowRDDMatrix
0d1491c [Xiangrui Meng] fix test errors
a85262a [Xiangrui Meng] rename RDDMatrixRow to IndexedRDDMatrixRow
b8b6ac3 [Xiangrui Meng] Remove old code
4cf679c [Xiangrui Meng] port pca to RowRDDMatrix, and add multiply and covariance
7836e2f [Xiangrui Meng] initial refactoring of matrices backed by RDDs
SPARK-1093: Annotate developer and experimental API's

This patch marks some existing classes as private[spark] and adds two types of API annotations:
- `EXPERIMENTAL API` = experimental user-facing module
- `DEVELOPER API - UNSTABLE` = developer-facing API that might change

There is some discussion of the different mechanisms for doing this here:
https://issues.apache.org/jira/browse/SPARK-1081

I was pretty aggressive with marking things private. Keep in mind that if we want to open something up in the future we can, but we can never reduce visibility.

A few notes here:
- In the past we've been inconsistent with the visiblity of the X-RDD classes. This patch marks them private whenever there is an existing function in RDD that can directly creat them (e.g. CoalescedRDD and rdd.coalesce()). One trade-off here is users can't subclass them.
- Noted that compression and serialization formats don't have to be wire compatible across versions.
- Compression codecs and serialization formats are semi-private as users typically don't instantiate them directly.
- Metrics sources are made private - user only interacts with them through Spark's reflection

Author: Patrick Wendell <pwendell@gmail.com>
Author: Andrew Or <andrewor14@gmail.com>

Closes #274 from pwendell/private-apis and squashes the following commits:

44179e4 [Patrick Wendell] Merge remote-tracking branch 'apache-github/master' into private-apis
042c803 [Patrick Wendell] spark.annotations -> spark.annotation
bfe7b52 [Patrick Wendell] Adding experimental for approximate counts
8d0c873 [Patrick Wendell] Warning in SparkEnv
99b223a [Patrick Wendell] Cleaning up annotations
e849f64 [Patrick Wendell] Merge pull request #2 from andrewor14/annotations
982a473 [Andrew Or] Generalize jQuery matching for non Spark-core API docs
a01c076 [Patrick Wendell] Merge pull request #1 from andrewor14/annotations
c1bcb41 [Andrew Or] DeveloperAPI -> DeveloperApi
0d48908 [Andrew Or] Comments and new lines (minor)
f3954e0 [Andrew Or] Add identifier tags in comments to work around scaladocs bug
99192ef [Andrew Or] Dynamically add badges based on annotations
824011b [Andrew Or] Add support for injecting arbitrary JavaScript to API docs
037755c [Patrick Wendell] Some changes after working with andrew or
f7d124f [Patrick Wendell] Small fixes
c318b24 [Patrick Wendell] Use CSS styles
e4c76b9 [Patrick Wendell] Logging
f390b13 [Patrick Wendell] Better visibility for workaround constructors
d6b0afd [Patrick Wendell] Small chang to existing constructor
403ba52 [Patrick Wendell] Style fix
870a7ba [Patrick Wendell] Work around for SI-8479
7fb13b2 [Patrick Wendell] Changes to UnionRDD and EmptyRDD
4a9e90c [Patrick Wendell] EXPERIMENTAL API --> EXPERIMENTAL
c581dce [Patrick Wendell] Changes after building against Shark.
8452309 [Patrick Wendell] Style fixes
1ed27d2 [Patrick Wendell] Formatting and coloring of badges
cd7a465 [Patrick Wendell] Code review feedback
2f706f1 [Patrick Wendell] Don't use floats
542a736 [Patrick Wendell] Small fixes
cf23ec6 [Patrick Wendell] Marking GraphX as alpha
d86818e [Patrick Wendell] Another naming change
5a76ed6 [Patrick Wendell] More visiblity clean-up
42c1f09 [Patrick Wendell] Using better labels
9d48cbf [Patrick Wendell] Initial pass
[SPARK-1357] [MLLIB] Annotate developer and experimental APIs

Annotate developer and experimental APIs in MLlib.

Author: Xiangrui Meng <meng@databricks.com>

Closes #298 from mengxr/api and squashes the following commits:

13390e8 [Xiangrui Meng] Merge branch 'master' into api
dc4cbb3 [Xiangrui Meng] mark distribute matrices experimental
6b9f8e2 [Xiangrui Meng] add Experimental annotation
8773d0d [Xiangrui Meng] add DeveloperApi annotation
da31733 [Xiangrui Meng] update developer and experimental tags
555e0fe [Xiangrui Meng] Merge branch 'master' into api
ef1a717 [Xiangrui Meng] mark some constructors private add default parameters to JavaDoc
00ffbcc [Xiangrui Meng] update tree API annotation
0b674fa [Xiangrui Meng] mark decision tree APIs
86b9e34 [Xiangrui Meng] one pass over APIs of GLMs, NaiveBayes, and ALS
f21d862 [Xiangrui Meng] Merge branch 'master' into api
2b133d6 [Xiangrui Meng] intial annotation of developer and experimental apis
SPARK-1407 drain event queue before stopping event logger

Author: Kan Zhang <kzhang@apache.org>

Closes #366 from kanzhang/SPARK-1407 and squashes the following commits:

cd0629f [Kan Zhang] code refactoring and adding test
b073ee6 [Kan Zhang] SPARK-1407 drain event queue before stopping event logger
[SPARK-1357 (fix)] remove empty line after :: DeveloperApi/Experimental ::

Remove empty line after :: DeveloperApi/Experimental :: in comments to make the original doc show up in the preview of the generated html docs. Thanks @andrewor14 !

Author: Xiangrui Meng <meng@databricks.com>

Closes #373 from mengxr/api and squashes the following commits:

9c35bdc [Xiangrui Meng] remove the empty line after :: DeveloperApi/Experimental ::
SPARK-729:  Closures not always serialized at capture time

[SPARK-729](https://spark-project.atlassian.net/browse/SPARK-729) concerns when free variables in closure arguments to transformations are captured.  Currently, it is possible for closures to get the environment in which they are serialized (not the environment in which they are created).  There are a few possible approaches to solving this problem and this PR will discuss some of them.  The approach I took has the advantage of being simple, obviously correct, and minimally-invasive, but it preserves something that has been bothering me about Spark's closure handling, so I'd like to discuss an alternative and get some feedback on whether or not it is worth pursuing.

## What I did

The basic approach I took depends on the work I did for #143, and so this PR is based atop that.  Specifically: #143 modifies `ClosureCleaner.clean` to preemptively determine whether or not closures are serializable immediately upon closure cleaning (rather than waiting for an job involving that closure to be scheduled).  Thus non-serializable closure exceptions will be triggered by the line defining the closure rather than triggered where the closure is used.

Since the easiest way to determine whether or not a closure is serializable is to attempt to serialize it, the code in #143 is creating a serialized closure as part of `ClosureCleaner.clean`.  `clean` currently modifies its argument, but the method in `SparkContext` that wraps it to return a value (a reference to the modified-in-place argument).  This branch modifies `ClosureCleaner.clean` so that it returns a value:  if it is cleaning a serializable closure, it returns the result of deserializing its serialized argument; therefore it is returning a closure with an environment captured at cleaning time.  `SparkContext.clean` then returns the result of `ClosureCleaner.clean`, rather than a reference to its modified-in-place argument.

I've added tests for this behavior (777a1bc).  The pull request as it stands, given the changes in #143, is nearly trivial.  There is some overhead from deserializing the closure, but it is minimal and the benefit of obvious operational correctness (vs. a more sophisticated but harder-to-validate transformation in `ClosureCleaner`) seems pretty important.  I think this is a fine way to solve this problem, but it's not perfect.

## What we might want to do

The thing that has been bothering me about Spark's handling of closures is that it seems like we should be able to statically ensure that cleaning and serialization happen exactly once for a given closure.  If we serialize a closure in order to determine whether or not it is serializable, we should be able to hang on to the generated byte buffer and use it instead of re-serializing the closure later.  By replacing closures with instances of a sum type that encodes whether or not a closure has been cleaned or serialized, we could handle clean, to-be-cleaned, and serialized closures separately with case matches.  Here's a somewhat-concrete sketch (taken from my git stash) of what this might look like:

```scala
package org.apache.spark.util

import java.nio.ByteBuffer
import scala.reflect.ClassManifest

sealed abstract class ClosureBox[T] { def func: T }
final case class RawClosure[T](func: T) extends ClosureBox[T] {}
final case class CleanedClosure[T](func: T) extends ClosureBox[T] {}
final case class SerializedClosure[T](func: T, bytebuf: ByteBuffer) extends ClosureBox[T] {}

object ClosureBoxImplicits {
  implicit def closureBoxFromFunc[T <: AnyRef](fun: T) = new RawClosure[T](fun)
}
```

With these types declared, we'd be able to change `ClosureCleaner.clean` to take a `ClosureBox[T=>U]` (possibly generated by implicit conversion) and return a `ClosureBox[T=>U]` (either a `CleanedClosure[T=>U]` or a `SerializedClosure[T=>U]`, depending on whether or not serializability-checking was enabled) instead of a `T=>U`.  A case match could thus short-circuit cleaning or serializing closures that had already been cleaned or serialized (both in `ClosureCleaner` and in the closure serializer).  Cleaned-and-serialized closures would be represented by a boxed tuple of the original closure and a serialized copy (complete with an environment quiesced at transformation time).  Additional implicit conversions could convert from `ClosureBox` instances to the underlying function type where appropriate.  Tracking this sort of state in the type system seems like the right thing to do to me.

### Why we might not want to do that

_It's pretty invasive._  Every function type used by every `RDD` subclass would have to change to reflect that they expected a `ClosureBox[T=>U]` instead of a `T=>U`.  This obscures what's going on and is not a little ugly.  Although I really like the idea of using the type system to enforce the clean-or-serialize once discipline, it might not be worth adding another layer of types (even if we could hide some of the extra boilerplate with judicious application of implicit conversions).

_It statically guarantees a property whose absence is unlikely to cause any serious problems as it stands._  It appears that all closures are currently dynamically cleaned once and it's not obvious that repeated closure-cleaning is likely to be a problem in the future.  Furthermore, serializing closures is relatively cheap, so doing it once to check for serialization and once again to actually ship them across the wire doesn't seem like a big deal.

Taken together, these seem like a high price to pay for statically guaranteeing that closures are operated upon only once.

## Other possibilities

I felt like the serialize-and-deserialize approach was best due to its obvious simplicity.  But it would be possible to do a more sophisticated transformation within `ClosureCleaner.clean`.  It might also be possible for `clean` to modify its argument in a way so that whether or not a given closure had been cleaned would be apparent upon inspection; this would buy us some of the operational benefits of the `ClosureBox` approach but not the static cleanliness.

I'm interested in any feedback or discussion on whether or not the problems with the type-based approach indeed outweigh the advantage, as well as of approaches to this issue and to closure handling in general.

Author: William Benton <willb@redhat.com>

Closes #189 from willb/spark-729 and squashes the following commits:

f4cafa0 [William Benton] Stylistic changes and cleanups
b3d9c86 [William Benton] Fixed style issues in tests
9b56ce0 [William Benton] Added array-element capture test
97e9d91 [William Benton] Split closure-serializability failure tests
12ef6e3 [William Benton] Skip proactive closure capture for runJob
8ee3ee7 [William Benton] Predictable closure environment capture
12c63a7 [William Benton] Added tests for variable capture in closures
d6e8dd6 [William Benton] Don't check serializability of DStream transforms.
4ecf841 [William Benton] Make proactive serializability checking optional.
d8df3db [William Benton] Adds proactive closure-serializablilty checking
21b4b06 [William Benton] Test cases for SPARK-897.
d5947b3 [William Benton] Ensure assertions in Graph.apply are asserted.
SPARK-1446: Spark examples should not do a System.exit

Spark examples should exit nice using SparkContext.stop() method, rather than System.exit
System.exit can cause issues like in SPARK-1407

Author: Sandeep <sandeep@techaddict.me>

Closes #370 from techaddict/1446 and squashes the following commits:

e9234cf [Sandeep] SPARK-1446: Spark examples should not do a System.exit Spark examples should exit nice using SparkContext.stop() method, rather than System.exit System.exit can cause issues like in SPARK-1407
Revert "SPARK-729:  Closures not always serialized at capture time"

This reverts commit 8ca3b2bc90a63b23a03f339e390174cd7a672b40.
Fix SPARK-1413: Parquet messes up stdout and stdin when used in Spark REPL

Author: witgo <witgo@qq.com>

Closes #325 from witgo/SPARK-1413 and squashes the following commits:

e57cd8e [witgo] use scala reflection to access and call the SLF4JBridgeHandler  methods
45c8f40 [witgo] Merge branch 'master' of https://github.com/apache/spark into SPARK-1413
5e35d87 [witgo] Merge branch 'master' of https://github.com/apache/spark into SPARK-1413
0d5f819 [witgo] review commit
45e5b70 [witgo] Merge branch 'master' of https://github.com/apache/spark into SPARK-1413
fa69dcf [witgo] Merge branch 'master' into SPARK-1413
3c98dc4 [witgo] Merge branch 'master' into SPARK-1413
38160cb [witgo] Merge branch 'master' of https://github.com/apache/spark into SPARK-1413
ba09bcd [witgo] remove set the parquet log level
a63d574 [witgo] Merge branch 'master' of https://github.com/apache/spark into SPARK-1413
5231ecd [witgo] Merge branch 'master' of https://github.com/apache/spark into SPARK-1413
3feb635 [witgo] parquet logger use parent handler
fa00d5d [witgo] Merge branch 'master' of https://github.com/apache/spark into SPARK-1413
8bb6ffd [witgo] enableLogForwarding note fix
edd9630 [witgo]  move to
f447f50 [witgo] merging master
5ad52bd [witgo] Merge branch 'master' of https://github.com/apache/spark into SPARK-1413
76670c1 [witgo] review commit
70f3c64 [witgo] Fix SPARK-1413
[SPARK-1276] Add a HistoryServer to render persisted UI

The new feature of event logging, introduced in #42, allows the user to persist the details of his/her Spark application to storage, and later replay these events to reconstruct an after-the-fact SparkUI.
Currently, however, a persisted UI can only be rendered through the standalone Master. This greatly limits the use case of this new feature as many people also run Spark on Yarn / Mesos.

This PR introduces a new entity called the HistoryServer, which, given a log directory, keeps track of all completed applications independently of a Spark Master. Unlike Master, the HistoryServer needs not be running while the application is still running. It is relatively light-weight in that it only maintains static information of applications and performs no scheduling.

To quickly test it out, generate event logs with ```spark.eventLog.enabled=true``` and run ```sbin/start-history-server.sh <log-dir-path>```. Your HistoryServer awaits on port 18080.

Comments and feedback are most welcome.

---

A few other changes introduced in this PR include refactoring the WebUI interface, which is beginning to have a lot of duplicate code now that we have added more functionality to it. Two new SparkListenerEvents have been introduced (SparkListenerApplicationStart/End) to keep track of application name and start/finish times. This PR also clarifies the semantics of the ReplayListenerBus introduced in #42.

A potential TODO in the future (not part of this PR) is to render live applications in addition to just completed applications. This is useful when applications fail, a condition that our current HistoryServer does not handle unless the user manually signals application completion (by creating the APPLICATION_COMPLETION file). Handling live applications becomes significantly more challenging, however, because it is now necessary to render the same SparkUI multiple times. To avoid reading the entire log every time, which is inefficient, we must handle reading the log from where we previously left off, but this becomes fairly complicated because we must deal with the arbitrary behavior of each input stream.

Author: Andrew Or <andrewor14@gmail.com>

Closes #204 from andrewor14/master and squashes the following commits:

7b7234c [Andrew Or] Finished -> Completed
b158d98 [Andrew Or] Address Patrick's comments
69d1b41 [Andrew Or] Do not block on posting SparkListenerApplicationEnd
19d5dd0 [Andrew Or] Merge github.com:apache/spark
f7f5bf0 [Andrew Or] Make history server's web UI port a Spark configuration
2dfb494 [Andrew Or] Decouple checking for application completion from replaying
d02dbaa [Andrew Or] Expose Spark version and include it in event logs
2282300 [Andrew Or] Add documentation for the HistoryServer
567474a [Andrew Or] Merge github.com:apache/spark
6edf052 [Andrew Or] Merge github.com:apache/spark
19e1fb4 [Andrew Or] Address Thomas' comments
248cb3d [Andrew Or] Limit number of live applications + add configurability
a3598de [Andrew Or] Do not close file system with ReplayBus + fix bind address
bc46fc8 [Andrew Or] Merge github.com:apache/spark
e2f4ff9 [Andrew Or] Merge github.com:apache/spark
050419e [Andrew Or] Merge github.com:apache/spark
81b568b [Andrew Or] Fix strange error messages...
0670743 [Andrew Or] Decouple page rendering from loading files from disk
1b2f391 [Andrew Or] Minor changes
a9eae7e [Andrew Or] Merge branch 'master' of github.com:apache/spark
d5154da [Andrew Or] Styling and comments
5dbfbb4 [Andrew Or] Merge branch 'master' of github.com:apache/spark
60bc6d5 [Andrew Or] First complete implementation of HistoryServer (only for finished apps)
7584418 [Andrew Or] Report application start/end times to HistoryServer
8aac163 [Andrew Or] Add basic application table
c086bd5 [Andrew Or] Add HistoryServer and scripts ++ Refactor WebUI interface
SPARK-1428: MLlib should convert non-float64 NumPy arrays to float64 instead of complaining

Author: Sandeep <sandeep@techaddict.me>

Closes #356 from techaddict/1428 and squashes the following commits:

3bdf5f6 [Sandeep] SPARK-1428: MLlib should convert non-float64 NumPy arrays to float64 instead of complaining
Revert "SPARK-1433: Upgrade Mesos dependency to 0.17.0"

This reverts commit 12c077d5aa0b76a808a55db625c9677a52bd43f9.
Update tuning.md

http://stackoverflow.com/questions/9699071/what-is-the-javas-internal-represention-for-string-modified-utf-8-utf-16

Author: Andrew Ash <andrew@andrewash.com>

Closes #384 from ash211/patch-2 and squashes the following commits:

da1b0be [Andrew Ash] Update tuning.md
Remove Unnecessary Whitespace's

stack these together in a commit else they show up chunk by chunk in different commits.

Author: Sandeep <sandeep@techaddict.me>

Closes #380 from techaddict/white_space and squashes the following commits:

b58f294 [Sandeep] Remove Unnecessary Whitespace's
[SQL] Improve column pruning in the optimizer.

Author: Michael Armbrust <michael@databricks.com>

Closes #378 from marmbrus/columnPruning and squashes the following commits:

779da56 [Michael Armbrust] More consistent naming.
1a4e9ea [Michael Armbrust] More comments.
2f4e7b9 [Michael Armbrust] Improve column pruning in the optimizer.
SPARK-1202 - Add a "cancel" button in the UI for stages

Author: Sundeep Narravula <sundeepn@superduel.local>
Author: Sundeep Narravula <sundeepn@dhcpx-204-110.corp.yahoo.com>

Closes #246 from sundeepn/uikilljob and squashes the following commits:

5fdd0e2 [Sundeep Narravula] Fix test string
f6fdff1 [Sundeep Narravula] Format fix; reduced line size to less than 100 chars
d1daeb9 [Sundeep Narravula] Incorporating review comments.
8d97923 [Sundeep Narravula] Ability to kill jobs thru the UI. This behavior can be turned on be settings the following variable: spark.ui.killEnabled=true (default=false) Adding DAGScheduler event StageCancelled and corresponding handlers. Added cancellation reason to handlers.
Set spark.executor.uri from environment variable (needed by Mesos)

The Mesos backend uses this property when setting up a slave process.  It is similarly set in the Scala repl (org.apache.spark.repl.SparkILoop), but I couldn't find any analogous for pyspark.

Author: Ivan Wick <ivanwick+github@gmail.com>

This patch had conflicts when merged, resolved by
Committer: Matei Zaharia <matei@databricks.com>

Closes #311 from ivanwick/master and squashes the following commits:

da0c3e4 [Ivan Wick] Set spark.executor.uri from environment variable (needed by Mesos)
Add Spark v0.9.1 to ec2 launch script and use it as the default

Mainly ported from branch-0.9.

Author: Harvey Feng <hyfeng224@gmail.com>

Closes #385 from harveyfeng/0.9.1-ec2 and squashes the following commits:

769ac2f [Harvey Feng] Add Spark v0.9.1 to ec2 launch script and use it as the default
SPARK-1202: Improvements to task killing in the UI.

1. Adds a separate endpoint for the killing logic that is outside of a page.
2. Narrows the scope of the killingEnabled tracking.
3. Some style improvements.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #386 from pwendell/kill-link and squashes the following commits:

8efe02b [Patrick Wendell] Improvements to task killing in the UI.