Python api additions

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

== Merge branch commits ==

commit 8b51591f1a7a79a62c13ee66ff8d83040f7eccd8
Author: Prashant Sharma <prashant.s@imaginea.com>
Date:   Fri Jan 24 11:50:29 2014 +0530

    Josh's and Patricks review comments.

commit d37f9677838e43bef6c18ef61fbf08055ba6d1ca
Author: Prashant Sharma <prashant.s@imaginea.com>
Date:   Thu Jan 23 17:27:17 2014 +0530

    fixed doc tests

commit 27cb54bf5c99b1ea38a73858c291d0a1c43d8b7c
Author: Prashant Sharma <prashant.s@imaginea.com>
Date:   Thu Jan 23 16:48:43 2014 +0530

    Added keys and values methods for PairFunctions in python

commit 4ce76b396fbaefef2386d7a36d611572bdef9b5d
Author: Prashant Sharma <prashant.s@imaginea.com>
Date:   Thu Jan 23 13:51:26 2014 +0530

    Added foreachPartition

commit 05f05341a187cba829ac0e6c2bdf30be49948c89
Author: Prashant Sharma <prashant.s@imaginea.com>
Date:   Thu Jan 23 13:02:59 2014 +0530

    Added coalesce fucntion to python API

commit 6568d2c2fa14845dc56322c0f39ba2e13b3b26dd
Author: Prashant Sharma <prashant.s@imaginea.com>
Date:   Thu Jan 23 12:52:44 2014 +0530

    added repartition function to python API.

This fixes SPARK-1043, a bug introduced in 0.9.0
where PySpark couldn't serialize strings > 64kB.

This fix was written by @tyro89 and @bouk in #512.
This commit squashes and rebases their pull request
in order to fix some merge conflicts.

Also, replace the last reference to it in the docs.

This fixes SPARK-1026.

Remove Typesafe Config usage and conf files to fix nested property names

With Typesafe Config we had the subtle problem of no longer allowing
nested property names, which are used for a few of our properties:
http://apache-spark-developers-list.1001551.n3.nabble.com/Config-properties-broken-in-master-td208.html



This PR is for branch 0.9 but should be added into master too.
(cherry picked from commit 34e911ce)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>

This helps in case the exception happened while serializing a record to
be sent to Java, leaving the stream to Java in an inconsistent state
where PythonRDD won't be able to read the error.

We've used camel case in other Spark methods so it felt reasonable to
keep using it here and make the code match Scala/Java as much as
possible. Note that parameter names matter in Python because it allows
passing optional parameters by name.

- Added a Python wrapper for Naive Bayes
- Updated the Scala Naive Bayes to match the style of our other
  algorithms better and in particular make it easier to call from Java
  (added builder pattern, removed default value in train method)
- Updated Python MLlib functions to not require a SparkContext; we can
  get that from the RDD the user gives
- Added a toString method in LabeledPoint
- Made the Python MLlib tests run as part of run-tests as well (before
  they could only be run individually through each file)

Closes #316

Also replaced SparkConf.getOrElse with just a "get" that takes a default
value, and added getInt, getLong, etc to make code that uses this
simpler later on.

tests so we don't get the test spark.conf on the classpath.

The test in context.py created two different instances of the
SparkContext class by copying "globals", so that some tests can have a
global "sc" object and others can try initializing their own contexts.
This led to two JVM gateways being created since SparkConf also looked
at pyspark.context.SparkContext to get the JVM.