added SPARK_WORKER_INSTANCES : allows spawning multiple worker instances/processes on every slave machine

Re-enable deprecation warnings and fix deprecated warning.

Make Executor fields volatile since they're read from the thread pool.

mapWith, flatMapWith and filterWith

SPARK-715: Adds instructions for building with Maven to documentation

Added mapSideCombine flag to CoGroupedRDD. Added unit test for CoGroupedRDD.

[SPARK-707] Adding Java versions of Pi, LogQuery and K-Means examples

Add foldByKey

CoGroupedRDD.

CoalescedRDD for many partitions

Remove try/catch block that can't be hit.

call setConf from input format if it is Configurable

CoalescedRDD changed to work with a big number of partitions both in the original and the new coalesced RDD.
The limitation was in the range that Scala.Int can represent.

Adds links to new instructions in:
* The main Spark project README.md
* The docs nav menu called "More"
* The docs Overview page under the "Building" and "Where to Go from Here" sections

Add PairRDDFunctions.subtractByKey.