Added partition aware union to improve reduceByKeyAndWindow
Added partitioner aware union, modified DStream.window.
Added flag in window operation to use partition awaare union.
Merge branch 'scheduler-update' into window-improvement

Conflicts:
	streaming/src/main/scala/org/apache/spark/streaming/dstream/WindowedDStream.scala
Added tests for PartitionerAwareUnionRDD in the CheckpointSuite. Refactored CheckpointSuite to make the tests simpler and more reliable. Added missing test for ZippedRDD.
Merge branch 'scheduler-update' into window-improvement
spark-544, introducing SparkConf and related configuration overhaul.
Fixed bug in PartitionAwareUnionRDD
Updated groupByKeyAndWindow to be computed incrementally, and added mapSideCombine to combineByKeyAndWindow.
Merge branch 'master' into window-improvement
Merge branch 'apache-master' into window-improvement
Removed unncessary options from WindowedDStream.
Added Apache boilerplate and class docs to PartitionerAwareUnionRDD.
Various fixes to configuration code

- Got rid of global SparkContext.globalConf
- Pass SparkConf to serializers and compression codecs
- Made SparkConf public instead of private[spark]
- Improved API of SparkContext and SparkConf
- Switched executor environment vars to be passed through SparkConf
- Fixed some places that were still using system properties
- Fixed some tests, though others are still failing

This still fails several tests in core, repl and streaming, likely due
to properties not being set or cleared correctly (some of the tests run
fine in isolation).
Check for SPARK_YARN_MODE through a system property too since it can
sometimes be set that way (undoes a change in previous commit)
Fix Executor not getting properties in local mode
Fix test failures due to setting / clearing clock type in Streaming
Fix CheckpointSuite test failures
Add a StreamingContext constructor that takes a conf object
Fix other failing tests