Added a serializable wrapper for HyperLogLog
Added a countDistinct method to RDD that takes takes an accuracy parameter and returns the (approximate) number of distinct elements in the RDD.
Added countDistinctByKey to PairRDDFunctions that counts the approximate number of unique values for each key in the RDD.
Added dependency on stream-lib version 2.4.0 for approximate distinct count support.
Fixed document typo
Improved code style.
Added stream-lib dependency to Maven build
Made SerializableHyperLogLog Externalizable and added Kryo tests
Added partition aware union to improve reduceByKeyAndWindow
Added partitioner aware union, modified DStream.window.
Added flag in window operation to use partition awaare union.
Removed superfluous abs call from test cases.
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.
upgrade Netty from 4.0.0.Beta2 to 4.0.13.Final
Remove import * and fix some formatting
Fix imports order
Fixed bug in PartitionAwareUnionRDD