[SPARK-2952] Enable logging actor messages at DEBUG level

Example messages:
```
14/08/09 21:37:01 DEBUG BlockManagerMasterActor: [actor] received message RegisterBlockManager(BlockManagerId(0, rxin-mbp, 58092, 0),278302556,Actor[akka.tcp://spark@rxin-mbp:58088/user/BlockManagerActor1#-63596539]) from Actor[akka.tcp://spark@rxin-mbp:58088/temp/$c]

14/08/09 21:37:01 DEBUG BlockManagerMasterActor: [actor] handled message (0.279 ms) RegisterBlockManager(BlockManagerId(0, rxin-mbp, 58092, 0),278302556,Actor[akka.tcp://spark@rxin-mbp:58088/user/BlockManagerActor1#-63596539]) from Actor[akka.tcp://spark@rxin-mbp:58088/temp/$c]
```

cc @mengxr @tdas @pwendell

Author: Reynold Xin <rxin@apache.org>

Closes #1870 from rxin/actorLogging and squashes the following commits:

c531ee5 [Reynold Xin] Added license header for ActorLogReceive.
f6b1ebe [Reynold Xin] [SPARK-2952] Enable logging actor messages at DEBUG level
[SPARK-2931] In TaskSetManager, reset currentLocalityIndex after recomputing locality levels

This addresses SPARK-2931, a bug where getAllowedLocalityLevel() could throw ArrayIndexOutOfBoundsException.  The fix here is to reset currentLocalityIndex after recomputing the locality levels.

Thanks to kayousterhout, mridulm, and lirui-intel for helping me to debug this.

Author: Josh Rosen <joshrosen@apache.org>

Closes #1896 from JoshRosen/SPARK-2931 and squashes the following commits:

48b60b5 [Josh Rosen] Move FakeRackUtil.cleanUp() info beforeEach().
6fec474 [Josh Rosen] Set currentLocalityIndex after recomputing locality levels.
9384897 [Josh Rosen] Update SPARK-2931 test to reflect changes in 63bdb1f41b4895e3a9444f7938094438a94d3007.
9ecd455 [Josh Rosen] Apply @mridulm's patch for reproducing SPARK-2931.
[SPARK-2515][mllib] Chi Squared test

Author: Doris Xin <doris.s.xin@gmail.com>

Closes #1733 from dorx/chisquare and squashes the following commits:

cafb3a7 [Doris Xin] fixed p-value for extreme case.
d286783 [Doris Xin] Merge branch 'master' into chisquare
e95e485 [Doris Xin] reviewer comments.
7dde711 [Doris Xin] ChiSqTestResult renaming and changed to Class
80d03e2 [Doris Xin] Reviewer comments.
c39eeb5 [Doris Xin] units passed with updated API
e90d90a [Doris Xin] Merge branch 'master' into chisquare
7eea80b [Doris Xin] WIP
d64c2fb [Doris Xin] Merge branch 'master' into chisquare
5686082 [Doris Xin] facelift
bc7eb2e [Doris Xin] unit passed; still need docs and some refactoring
50703a5 [Doris Xin] merge master
4e4e361 [Doris Xin] WIP
e6b83f3 [Doris Xin] reviewer comments
3d61582 [Doris Xin] input names
706d436 [Doris Xin] Added API for RDD[Vector]
6598379 [Doris Xin] API and code structure.
ff17423 [Doris Xin] WIP
[SPARK-2934][MLlib] Adding LogisticRegressionWithLBFGS Interface

for training with LBFGS Optimizer which will converge faster than SGD.

Author: DB Tsai <dbtsai@alpinenow.com>

Closes #1862 from dbtsai/dbtsai-lbfgs-lor and squashes the following commits:

aa84b81 [DB Tsai] small change
f852bcd [DB Tsai] Remove duplicate method
f119fdc [DB Tsai] Formatting
97776aa [DB Tsai] address more feedback
85b4a91 [DB Tsai] address feedback
3cf50c2 [DB Tsai] LogisticRegressionWithLBFGS interface
[SPARK-2844][SQL] Correctly set JVM HiveContext if it is passed into Python HiveContext constructor

https://issues.apache.org/jira/browse/SPARK-2844

Author: Ahir Reddy <ahirreddy@gmail.com>

Closes #1768 from ahirreddy/python-hive-context-fix and squashes the following commits:

7972d3b [Ahir Reddy] Correctly set JVM HiveContext if it is passed into Python HiveContext constructor
[SPARK-2590][SQL] Added option to handle incremental collection, disabled by default

JIRA issue: [SPARK-2590](https://issues.apache.org/jira/browse/SPARK-2590)

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

Closes #1853 from liancheng/inc-collect-option and squashes the following commits:

cb3ea45 [Cheng Lian] Moved incremental collection option to Thrift server
43ce3aa [Cheng Lian] Changed incremental collect option name
623abde [Cheng Lian] Added option to handle incremental collection, disabled by default
[sql]use SparkSQLEnv.stop() in ShutdownHook

Author: wangfei <wangfei1@huawei.com>

Closes #1852 from scwf/patch-3 and squashes the following commits:

ae28c29 [wangfei] use SparkSQLEnv.stop() in ShutdownHook
[SQL] A tiny refactoring in HiveContext#analyze

I should use `EliminateAnalysisOperators` in  `analyze` instead of manually pattern matching.

Author: Yin Huai <huaiyin.thu@gmail.com>

Closes #1881 from yhuai/useEliminateAnalysisOperators and squashes the following commits:

f3e1e7f [Yin Huai] Use EliminateAnalysisOperators.
[SPARK-2965][SQL] Fix HashOuterJoin output nullabilities.

Output attributes of opposite side of `OuterJoin` should be nullable.

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

Closes #1887 from ueshin/issues/SPARK-2965 and squashes the following commits:

bcb2d37 [Takuya UESHIN] Fix HashOuterJoin output nullabilities.
[SPARK-2968][SQL] Fix nullabilities of Explode.

Output nullabilities of `Explode` could be detemined by `ArrayType.containsNull` or `MapType.valueContainsNull`.

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

Closes #1888 from ueshin/issues/SPARK-2968 and squashes the following commits:

d128c95 [Takuya UESHIN] Fix nullability of Explode.