SPARK-2186: Spark SQL DSL support for simple aggregations such as SUM and AVG

**Description** This patch enables using the `.select()` function in SchemaRDD with functions such as `Sum`, `Count` and other.
**Testing** Unit tests added.

Author: Ximo Guanter Gonzalbez <ximo@tid.es>

Closes #1211 from edrevo/add-expression-support-in-select and squashes the following commits:

fe4a1e1 [Ximo Guanter Gonzalbez] Extend SQL DSL to functions
e1d344a [Ximo Guanter Gonzalbez] SPARK-2186: Spark SQL DSL support for simple aggregations such as SUM and AVG
[SPARK-2328] [SQL] Add execution of `SHOW TABLES` before `TestHive.reset()`.

`PruningSuite` is executed first of Hive tests unfortunately, `TestHive.reset()` breaks the test environment.
To prevent this, we must run a query before calling reset the first time.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1268 from ueshin/issues/SPARK-2328 and squashes the following commits:

043ceac [Takuya UESHIN] Add execution of `SHOW TABLES` before `TestHive.reset()`.
[SPARK-2287] [SQL] Make ScalaReflection be able to handle Generic case classes.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1226 from ueshin/issues/SPARK-2287 and squashes the following commits:

32ef7c3 [Takuya UESHIN] Add execution of `SHOW TABLES` before `TestHive.reset()`.
541dc8d [Takuya UESHIN] Merge branch 'master' into issues/SPARK-2287
fac5fae [Takuya UESHIN] Remove unnecessary method receiver.
d306e60 [Takuya UESHIN] Merge branch 'master' into issues/SPARK-2287
7de5706 [Takuya UESHIN] Make ScalaReflection be able to handle Generic case classes.
[SPARK-2324] SparkContext should not exit directly when spark.local.dir is a list of multiple paths and one of them has error

The spark.local.dir is configured as a list of multiple paths as follows /data1/sparkenv/local,/data2/sparkenv/local. If the disk data2 of the driver node has error, the application will exit since DiskBlockManager exits directly at createLocalDirs. If the disk data2 of the worker node has error, the executor will exit either.
DiskBlockManager should not exit directly at createLocalDirs if one of spark.local.dir has error. Since spark.local.dir has multiple paths, a problem should not affect the overall situation.
I think DiskBlockManager could ignore the bad directory at createLocalDirs.

Author: yantangzhai <tyz0303@163.com>

Closes #1274 from YanTangZhai/SPARK-2324 and squashes the following commits:

609bf48 [yantangzhai] [SPARK-2324] SparkContext should not exit directly when spark.local.dir is a list of multiple paths and one of them has error
df08673 [yantangzhai] [SPARK-2324] SparkContext should not exit directly when spark.local.dir is a list of multiple paths and one of them has error
[SPARK] Fix NPE for ExternalAppendOnlyMap

It did not handle null keys very gracefully before.

Author: Andrew Or <andrewor14@gmail.com>

Closes #1288 from andrewor14/fix-external and squashes the following commits:

312b8d8 [Andrew Or] Abstract key hash code
ed5adf9 [Andrew Or] Fix NPE for ExternalAppendOnlyMap
SPARK-1675. Make clear whether computePrincipalComponents requires centered data

Just closing out this small JIRA, resolving with a comment change.

Author: Sean Owen <sowen@cloudera.com>

Closes #1171 from srowen/SPARK-1675 and squashes the following commits:

45ee9b7 [Sean Owen] Add simple note that data need not be centered for computePrincipalComponents
[SPARK-2342] Evaluation helper's output type doesn't conform to input ty...

The function cast doesn't conform to the intention of "Those expressions are supposed to be in the same data type, and also the return type." comment

Author: Yijie Shen <henry.yijieshen@gmail.com>

Closes #1283 from yijieshen/master and squashes the following commits:

c7aaa4b [Yijie Shen] [SPARK-2342] Evaluation helper's output type doesn't conform to input type
[SPARK-2109] Setting SPARK_MEM for bin/pyspark does not work.

Trivial fix.

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #1050 from ScrapCodes/SPARK-2109/pyspark-script-bug and squashes the following commits:

77072b9 [Prashant Sharma] Changed echos to redirect to STDERR.
13f48a0 [Prashant Sharma] [SPARK-2109] Setting SPARK_MEM for bin/pyspark does not work.
[HOTFIX] Synchronize on SQLContext.settings in tests.

Let's see if this fixes the ongoing series of test failures in a master build machine (https://amplab.cs.berkeley.edu/jenkins/job/Spark-Master-SBT-pre-YARN/SPARK_HADOOP_VERSION=1.0.4,label=centos/81/).

pwendell marmbrus

Author: Zongheng Yang <zongheng.y@gmail.com>

Closes #1277 from concretevitamin/test-fix and squashes the following commits:

28c88bd [Zongheng Yang] Synchronize on SQLContext.settings in tests.
Streaming programming guide typos

Fix a bad Java code sample and a broken link in the streaming programming guide.

Author: Clément MATHIEU <clement@unportant.info>

Closes #1286 from cykl/streaming-programming-guide-typos and squashes the following commits:

b0908cb [Clément MATHIEU] Fix broken URL
9d3c535 [Clément MATHIEU] Spark streaming requires at least two working threads (scala version was OK)
[SPARK-1097] Workaround Hadoop conf ConcurrentModification issue

Workaround Hadoop conf ConcurrentModification issue

Author: Raymond Liu <raymond.liu@intel.com>

Closes #1273 from colorant/hadoopRDD and squashes the following commits:

994e98b [Raymond Liu] Address comments
e2cda3d [Raymond Liu] Workaround Hadoop conf ConcurrentModification issue
[SPARK-2350] Don't NPE while launching drivers

Prior to this change, we could throw a NPE if we launch a driver while another one is waiting, because removing from an iterator while iterating over it is not safe.

Author: Aaron Davidson <aaron@databricks.com>

Closes #1289 from aarondav/master-fail and squashes the following commits:

1cf1cf4 [Aaron Davidson] SPARK-2350: Don't NPE while launching drivers
[SPARK-2307][Reprise] Correctly report RDD blocks on SparkUI

**Problem.** The existing code in `ExecutorPage.scala` requires a linear scan through all the blocks to filter out the uncached ones. Every refresh could be expensive if there are many blocks and many executors.

**Solution.** The proper semantics should be the following: `StorageStatusListener` should contain only block statuses that are cached. This means as soon as a block is unpersisted by any mean, its status should be removed. This is reflected in the changes made in `StorageStatusListener.scala`.

Further, the `StorageTab` must stop relying on the `StorageStatusListener` changing a dropped block's status to `StorageLevel.NONE` (which no longer happens). This is reflected in the changes made in `StorageTab.scala` and `StorageUtils.scala`.

----------

If you have been following this chain of PRs like pwendell, you will quickly notice that this reverts the changes in #1249, which reverts the changes in #1080. In other words, we are adding back the changes from #1080, and fixing SPARK-2307 on top of those changes. Please ask questions if you are confused.

Author: Andrew Or <andrewor14@gmail.com>

Closes #1255 from andrewor14/storage-ui-fix-reprise and squashes the following commits:

45416fa [Andrew Or] Merge branch 'master' of github.com:apache/spark into storage-ui-fix-reprise
a82ea25 [Andrew Or] Add tests for StorageStatusListener
8773b01 [Andrew Or] Update comment / minor changes
3afde3f [Andrew Or] Correctly report the number of blocks on SparkUI
SPARK-2282: Reuse PySpark Accumulator sockets to avoid crashing Spark

JIRA: https://issues.apache.org/jira/browse/SPARK-2282

This issue is caused by a buildup of sockets in the TIME_WAIT stage of TCP, which is a stage that lasts for some period of time after the communication closes.

This solution simply allows us to reuse sockets that are in TIME_WAIT, to avoid issues with the buildup of the rapid creation of these sockets.

Author: Aaron Davidson <aaron@databricks.com>

Closes #1220 from aarondav/SPARK-2282 and squashes the following commits:

2e5cab3 [Aaron Davidson] SPARK-2282: Reuse PySpark Accumulator sockets to avoid crashing Spark
[SPARK-2059][SQL] Don't throw TreeNodeException in `execution.ExplainCommand`

This is a fix for the problem revealed by PR #1265.

Currently `HiveComparisonSuite` ignores output of `ExplainCommand` since Catalyst query plan is quite different from Hive query plan. But exceptions throw from `CheckResolution` still breaks test cases. This PR catches any `TreeNodeException` and reports it as part of the query explanation.

After merging this PR, PR #1265 can also be merged safely.

For a normal query:

```
scala> hql("explain select key from src").foreach(println)
...
[Physical execution plan:]
[HiveTableScan [key#9], (MetastoreRelation default, src, None), None]
```

For a wrong query with unresolved attribute(s):

```
scala> hql("explain select kay from src").foreach(println)
...
[Error occurred during query planning: ]
[Unresolved attributes: 'kay, tree:]
[Project ['kay]]
[ LowerCaseSchema ]
[  MetastoreRelation default, src, None]
```

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #1294 from liancheng/safe-explain and squashes the following commits:

4318911 [Cheng Lian] Don't throw TreeNodeException in `execution.ExplainCommand`
[SPARK-1199][REPL] Remove VALId and use the original import style for defined classes.

This is an alternate solution to #1176.

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #1179 from ScrapCodes/SPARK-1199/repl-fix-second-approach and squashes the following commits:

820b34b [Prashant Sharma] Here we generate two kinds of import wrappers based on whether it is a class or not.
Update SQLConf.scala

use concurrent.ConcurrentHashMap instead of util.Collections.synchronizedMap

Author: baishuo(白硕) <vc_java@hotmail.com>

Closes #1272 from baishuo/master and squashes the following commits:

51ec55d [baishuo(白硕)] Update SQLConf.scala
63da043 [baishuo(白硕)] Update SQLConf.scala
36b6dbd [baishuo(白硕)] Update SQLConf.scala
864faa0 [baishuo(白硕)] Update SQLConf.scala
593096b [baishuo(白硕)] Update SQLConf.scala
7304d9b [baishuo(白硕)] Update SQLConf.scala
843581c [baishuo(白硕)] Update SQLConf.scala
1d3e4a2 [baishuo(白硕)] Update SQLConf.scala
0740f28 [baishuo(白硕)] Update SQLConf.scala
[SPARK-2059][SQL] Add analysis checks

This replaces #1263 with a test case.

Author: Reynold Xin <rxin@apache.org>
Author: Michael Armbrust <michael@databricks.com>

Closes #1265 from rxin/sql-analysis-error and squashes the following commits:

a639e01 [Reynold Xin] Added a test case for unresolved attribute analysis.
7371e1b [Reynold Xin] Merge pull request #1263 from marmbrus/analysisChecks
448c088 [Michael Armbrust] Add analysis checks