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 'debug-class-not-found' into ooyala-nexus-publish
Update version to include debug-class-not-found fixes