1.change source abstract class to support MetricRegistry
2.change master/work/jvm source class

Scheduler code style cleanup.

SPARK-829: scheduler shouldn't hang if a task contains unserializable objects in its closure

Creates task start events

Made RegressionModel serializable and added unit tests to make sure predict methods would work.

Add a public method getCachedRdds to SparkContext

Creates Executors tab for Jobs UI

This is used to find methods in the Scala API that
need to be ported to the Java API.  To use it:

  ./run spark.tools.JavaAPICompletenessChecker
Conflicts:
	project/SparkBuild.scala
	run
	run2.cmd

Fix bug: DoubleRDDFunctions.sampleStdev() computed non-sample stdev()

Update JavaDoubleRDD to add new methods and docs.

Fixes SPARK-825.