STREAMING-50: Support transform workaround in JavaPairDStream

Update issue tracker link in contributing guide

This ports a useful workaround (the `transform` function) to
JavaPairDStream. It is necessary to do things like sorting which
are not supported yet in the core streaming API.

SPARK-694: All references to [K, V] in JavaDStreamLike should be changed to [K2, V2] 

SPARK-696: sortByKey should use 'ascending' parameter

to lack of memoization

Conflicts:
	core/src/main/scala/spark/scheduler/cluster/SparkDeploySchedulerBackend.scala
	core/src/main/scala/spark/scheduler/cluster/StandaloneSchedulerBackend.scala

Also fixes some issues in the rest of the code with detecting workers this way.

Conflicts:
	core/src/main/scala/spark/deploy/master/Master.scala
	core/src/main/scala/spark/deploy/worker/Worker.scala
	core/src/main/scala/spark/scheduler/cluster/SparkDeploySchedulerBackend.scala
	core/src/main/scala/spark/scheduler/cluster/StandaloneClusterMessage.scala
	core/src/main/scala/spark/scheduler/cluster/StandaloneSchedulerBackend.scala

Conflicts:
	docs/_config.yml

Conflicts:
	core/src/main/twirl/spark/deploy/master/index.scala.html
	core/src/main/twirl/spark/deploy/worker/index.scala.html

other issues

Conflicts:
	run2.cmd

Fixed a 404 in 'Tuning Spark' -- missing '.html'

add as many fetch requests as we can, subject to maxBytesInFlight

SPARK-678: Adding an example with an OLAP roll-up

Add RDD.coalesce, clean up some RDDs, other misc.

Add commutative requirement for 'reduce' to Python docstring.

Change docs on 'reduce' since the merging of local reduces no longer pre...

Conflicts:
	core/src/main/scala/spark/RDD.scala

SPARK-685 Adding IPYTHON environment variable support for launching pyspark using ...

ordering, so the reduce function must also be commutative.

Also made sure clearDependencies() was calling super, to ensure
the getSplits/getDependencies vars in the RDD base class get
cleaned up.

Also rename r->rdd and remove unneeded extra type info.