This builds on my earlier pull requests and turns on the explicit type checking in scalastyle.

Author: Reynold Xin <rxin@databricks.com>

Closes #5342 from rxin/SPARK-6428 and squashes the following commits:

7b531ab [Reynold Xin] import ordering
2d9a8a5 [Reynold Xin] jl
e668b1c [Reynold Xin] override
9b9e119 [Reynold Xin] Parenthesis.
82e0cf5 [Reynold Xin] [SPARK-6428] Turn on explicit type checking for public methods.

Author: Reynold Xin <rxin@databricks.com>

Closes #5125 from rxin/core-explicit-type and squashes the following commits:

f471415 [Reynold Xin] Revert style checker changes.
81b66e4 [Reynold Xin] Code review feedback.
a7533e3 [Reynold Xin] Mima excludes.
1d795f5 [Reynold Xin] [SPARK-6428] Added explicit types for all public methods in core.

Author: prudhvi <prudhvi953@gmail.com>

Closes #2799 from prudhvije/ScalaStyle/space-after-comment-start and squashes the following commits:

fc263a1 [prudhvi] [Core] Using scalastyle to check the space after comment start

...erators.

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

Closes #2358 from ScrapCodes/scalastyle-unicode and squashes the following commits:

12a20f2 [Prashant Sharma] [SPARK-2182] Scalastyle rule blocking (non keyboard typeable) unicode operators.

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

Closes #124 from ScrapCodes/SPARK-1096/scalastyle-comment-check and squashes the following commits:

214135a [Prashant Sharma] Review feedback.
5eba88c [Prashant Sharma] Fixed style checks for ///+ comments.
e54b2f8 [Prashant Sharma] improved message, work around.
83e7144 [Prashant Sharma] removed dependency on scalastyle in plugin, since scalastyle sbt plugin already depends on the right version. Incase we update the plugin we will have to adjust our spark-style project to depend on right scalastyle version.
810a1d6 [Prashant Sharma] SPARK-1096, a space after comment style checker.
ba33193 [Prashant Sharma] scala style as a project

SPARK-1058, Fix Style Errors and Add Scala Style to Spark Build. Pt 2

Continuation of PR #557

With this all scala style errors are fixed across the code base !!

The reason for creating a separate PR was to not interrupt an already reviewed and ready to merge PR. Hope this gets reviewed soon and merged too.

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

Closes #567 and squashes the following commits:

3b1ec30 [Prashant Sharma] scala style fixes

SPARK-1058, Fix Style Errors and Add Scala Style to Spark Build.

Author: Patrick Wendell <pwendell@gmail.com>
Author: Prashant Sharma <scrapcodes@gmail.com>

== Merge branch commits ==

commit 1a8bd1c059b842cb95cc246aaea74a79fec684f4
Author: Prashant Sharma <scrapcodes@gmail.com>
Date:   Sun Feb 9 17:39:07 2014 +0530

    scala style fixes

commit f91709887a8e0b608c5c2b282db19b8a44d53a43
Author: Patrick Wendell <pwendell@gmail.com>
Date:   Fri Jan 24 11:22:53 2014 -0800

    Adding scalastyle snapshot