SPARK-1321 Use Guava's top k implementation rather than our BoundedPriorityQueue based implementation

Also updated the documentation for top and takeOrdered.

On my simple test of sorting 100 million (Int, Int) tuples using Spark, Guava's top k implementation (in Ordering) is much faster than the BoundedPriorityQueue implementation for roughly sorted input (10 - 20X faster), and still faster for purely random input (2 - 5X).

Author: Reynold Xin <rxin@apache.org>

Closes #229 from rxin/takeOrdered and squashes the following commits:

0d11844 [Reynold Xin] Use Guava's top k implementation rather than our BoundedPriorityQueue based implementation. Also updated the documentation for top and takeOrdered.
SPARK-1322, top in pyspark should sort result in descending order.

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

Closes #235 from ScrapCodes/SPARK-1322/top-rev-sort and squashes the following commits:

f316266 [Prashant Sharma] Minor change in comment.
58e58c6 [Prashant Sharma] SPARK-1322, top in pyspark should sort result in descending order.
Unified package definition format in Spark SQL

According to discussions in comments of PR #208, this PR unifies package definition format in Spark SQL.

Some broken links in ScalaDoc and typos detected along the way are also fixed.

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

Closes #225 from liancheng/packageDefinition and squashes the following commits:

75c47b3 [Cheng Lian] Fixed file line length
4f87968 [Cheng Lian] Unified package definition format in Spark SQL
[SQL] Un-ignore a test that is now passing.

Add golden answer for aforementioned test.

Also, fix golden test generation from sbt/sbt by setting the classpath correctly.

Author: Michael Armbrust <michael@databricks.com>

Closes #244 from marmbrus/partTest and squashes the following commits:

37a33c9 [Michael Armbrust] Un-ignore a test that is now passing, add golden answer for aforementioned test.  Fix golden test generation from sbt/sbt.
[SQL] Add a custom serializer for maps since they do not have a no-arg constructor.

Author: Michael Armbrust <michael@databricks.com>

Closes #243 from marmbrus/mapSer and squashes the following commits:

54045f7 [Michael Armbrust] Add a custom serializer for maps since they do not have a no-arg constructor.
SPARK-1324: SparkUI Should Not Bind to SPARK_PUBLIC_DNS

/cc @aarondav and @andrewor14

Author: Patrick Wendell <pwendell@gmail.com>

Closes #231 from pwendell/ui-binding and squashes the following commits:

e8025f8 [Patrick Wendell] SPARK-1324: SparkUI Should Not Bind to SPARK_PUBLIC_DNS
Spark 1095 : Adding explicit return types to all public methods

Excluded those that are self-evident and the cases that are discussed in the mailing list.

Author: NirmalReddy <nirmal_reddy2000@yahoo.com>
Author: NirmalReddy <nirmal.reddy@imaginea.com>

Closes #168 from NirmalReddy/Spark-1095 and squashes the following commits:

ac54b29 [NirmalReddy] import misplaced
8c5ff3e [NirmalReddy] Changed syntax of unit returning methods
02d0778 [NirmalReddy] fixed explicit types in all the other packages
1c17773 [NirmalReddy] fixed explicit types in core package
SPARK-1325. The maven build error for Spark Tools

This is just a slight variation on https://github.com/apache/spark/pull/234 and alternative suggestion for SPARK-1325. `scala-actors` is not necessary. `SparkBuild.scala` should be updated to reflect the direct dependency on `scala-reflect` and `scala-compiler`. And the `repl` build, which has the same dependencies, should also be consistent between Maven / SBT.

Author: Sean Owen <sowen@cloudera.com>
Author: witgo <witgo@qq.com>

Closes #240 from srowen/SPARK-1325 and squashes the following commits:

25bd7db [Sean Owen] Add necessary dependencies scala-reflect and scala-compiler to tools. Update repl dependencies, which are similar, to be consistent between Maven / SBT in this regard too.
Merge branch 'master' of https://github.com/apache/spark into SPARK-1325
 Merge master