Print out the class that was not found
Fix bug where classes in jars added via addJar() are not available to the driver

Adds a driver-specific class loader that knows about the jars added via addJar(), and
initialize it first thing in SparkEnv, so that all other ThreadPool/ActorSystem
initialization will take advantage of the classloader, and user-added jars are
made available to all Spark subsystems.
Merge branch 'master' into debug-class-not-found

Conflicts:
	core/src/main/scala/org/apache/spark/scheduler/TaskResultGetter.scala
Move classLoader initialization to SparkContext

SparkEnv is used by Executor as well; we want this change to affect driver only.
Pass the current class loader when creating Akka threadpool
CR from pwendell
Merge branch 'master' into debug-class-not-found

Conflicts:
	core/src/main/scala/org/apache/spark/SparkContext.scala
	core/src/main/scala/org/apache/spark/SparkEnv.scala
	core/src/main/scala/org/apache/spark/util/AkkaUtils.scala
CR: Rename ExecutorURLClassLoader -> SparkURLClassLoader
Use SparkURLClassLoader for driver only if spark.driver.add-dynamic-jars is set
Document new config option and effect on addJar
Merge remote-tracking branch 'apache/master' into addJars

Conflicts:
	core/src/main/scala/org/apache/spark/SparkContext.scala
	core/src/main/scala/org/apache/spark/SparkEnv.scala
	core/src/main/scala/org/apache/spark/util/AkkaUtils.scala
Minor changes
Adding unit tests.
Review feedback
Style fixes
Merge remote-tracking branch 'pwendell-origin/addJars' into SPARK-1230-SparkContext-addJars-classloader

Conflicts:
	core/src/main/scala/org/apache/spark/executor/Executor.scala
	core/src/test/scala/org/apache/spark/FileSuite.scala