[SPARK-2233] make-distribution script should list the git hash in the RELEASE file

This patch adds the git revision hash (short version) to the RELEASE file. It uses git instead of simply checking for the existence of .git, so as to make sure that this is a functional repository.

Author: Guillaume Ballet <gballet@gmail.com>

Closes #1216 from gballet/master and squashes the following commits:

eabc50f [Guillaume Ballet] Refactored the script to take comments into account.
d93e5e8 [Guillaume Ballet] [SPARK 2233] make-distribution script now lists the git hash tag in the RELEASE file.
[SPARK-1394] Remove SIGCHLD handler in worker subprocess

It should not be the responsibility of the worker subprocess, which
does not intentionally fork, to try and cleanup child processes. Doing
so is complex and interferes with operations such as
platform.system().

If it is desirable to have tighter control over subprocesses, then
namespaces should be used and it should be the manager's resposibility
to handle cleanup.

Author: Matthew Farrellee <matt@redhat.com>

Closes #1247 from mattf/SPARK-1394 and squashes the following commits:

c36f308 [Matthew Farrellee] [SPARK-1394] Remove SIGCHLD handler in worker subprocess
Improve MapOutputTracker error logging.

Author: Reynold Xin <rxin@apache.org>

Closes #1258 from rxin/mapOutputTracker and squashes the following commits:

a7c95b6 [Reynold Xin] Improve MapOutputTracker error logging.
[SPARK-2320] Reduce exception/code block font size in web ui

Author: Reynold Xin <rxin@apache.org>

Closes #1261 from rxin/ui-pre-size and squashes the following commits:

7ab1a69 [Reynold Xin] [SPARK-2320] Reduce exception/code block font size in web ui
[SPARK-1683] Track task read metrics.

This commit adds a new metric in TaskMetrics to record
the input data size and displays this information in the UI.

An earlier version of this commit also added the read time,
which can be useful for diagnosing straggler problems,
but unfortunately that change introduced a significant performance
regression for jobs that don't do much computation. In order to
track read time, we'll need to do sampling.

The screenshots below show the UI with the new "Input" field,
which I added to the stage summary page, the executor summary page,
and the per-stage page.

![image](https://cloud.githubusercontent.com/assets/1108612/3167930/2627f92a-eb77-11e3-861c-98ea5bb7a1a2.png)

![image](https://cloud.githubusercontent.com/assets/1108612/3167936/475a889c-eb77-11e3-9706-f11c48751f17.png)

![image](https://cloud.githubusercontent.com/assets/1108612/3167948/80ebcf12-eb77-11e3-87ed-349fce6a770c.png)

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #962 from kayousterhout/read_metrics and squashes the following commits:

f13b67d [Kay Ousterhout] Correctly format input bytes on executor page
8b70cde [Kay Ousterhout] Added comment about potential inaccuracy of bytesRead
d1016e8 [Kay Ousterhout] Udated SparkListenerSuite test
8461492 [Kay Ousterhout] Miniscule style fix
ae04d99 [Kay Ousterhout] Remove input metrics for parallel collections
719f19d [Kay Ousterhout] Style fixes
bb6ec62 [Kay Ousterhout] Small fixes
869ac7b [Kay Ousterhout] Updated Json tests
44a0301 [Kay Ousterhout] Fixed accidentally added line
4bd0568 [Kay Ousterhout] Added input source, renamed Hdfs to Hadoop.
f27e535 [Kay Ousterhout] Updates based on review comments and to fix rebase
bf41029 [Kay Ousterhout] Updated Json tests to pass
0fc33e0 [Kay Ousterhout] Added explicit backward compatibility test
4e52925 [Kay Ousterhout] Added Json output and associated tests.
365400b [Kay Ousterhout] [SPARK-1683] Track task read metrics.
[SPARK-2104] Fix task serializing issues when sort with Java non serializable class

Details can be see in [SPARK-2104](https://issues.apache.org/jira/browse/SPARK-2104). This work is based on Reynold's work, add some unit tests to validate the issue.

@rxin , would you please take a look at this PR, thanks a lot.

Author: jerryshao <saisai.shao@intel.com>

Closes #1245 from jerryshao/SPARK-2104 and squashes the following commits:

c8ee362 [jerryshao] Make field partitions transient
2b41917 [jerryshao] Minor changes
47d763c [jerryshao] Fix task serializing issue when sort with Java non serializable class
SPARK-897:  preemptively serialize closures

These commits cause `ClosureCleaner.clean` to attempt to serialize the cleaned closure with the default closure serializer and throw a `SparkException` if doing so fails.  This behavior is enabled by default but can be disabled at individual callsites of `SparkContext.clean`.

Commit 98e01ae8 fixes some no-op assertions in `GraphSuite` that this work exposed; I'm happy to put that in a separate PR if that would be more appropriate.

Author: William Benton <willb@redhat.com>

Closes #143 from willb/spark-897 and squashes the following commits:

bceab8a [William Benton] Commented DStream corner cases for serializability checking.
64d04d2 [William Benton] FailureSuite now checks both messages and causes.
3b3f74a [William Benton] Stylistic and doc cleanups.
b215dea [William Benton] Fixed spurious failures in ImplicitOrderingSuite
be1ecd6 [William Benton] Don't check serializability of DStream transforms.
abe816b [William Benton] Make proactive serializability checking optional.
5bfff24 [William Benton] Adds proactive closure-serializablilty checking
ed2ccf0 [William Benton] Test cases for SPARK-897.
SPARK-2077 Log serializer that actually ends up being used

I could settle with this being a debug also if we provided an example of how to turn it on in `log4j.properties`

https://issues.apache.org/jira/browse/SPARK-2077

Author: Andrew Ash <andrew@andrewash.com>

Closes #1017 from ash211/SPARK-2077 and squashes the following commits:

580f680 [Andrew Ash] Drop to debug
0266415 [Andrew Ash] SPARK-2077 Log serializer that actually ends up being used
Merge branch 'master' of https://github.com/apache/spark into SPARK-2098
add properties-file option