Minor cleanup.
Don't download files to master's working directory.

This should avoid exceptions caused by existing
files with different contents.

I also removed some unused code.
Add synchronization to Executor.updateDependencies() (SPARK-662)
Further simplify getOrElse call.
Make AccumulatorParam an abstract base class.
Refactor daemon thread pool creation.
Use generation numbers for fetch failure tracking
Fix for hanging spark.HttpFileServer with kind of virtual network
Handle slaveLost before slaveIdToHost knows about it.
Merge pull request #402 from stephenh/handleslavelosttoosoon

Handle slaveLost before slaveIdToHost knows about it.
Merge pull request #399 from NFLabs/master

Fix for hanging spark.HttpFileServer on the kind of virtual network
Fix sys.path bug in PySpark SparkContext.addPyFile
Add an Avro dependency to REPL to make it compile with Hadoop 2
Merge pull request #404 from mbautin/master-fix-avro-dependency-in-repl

Add an Avro dependency to REPL to make it compile with Hadoop 2
Merge pull request #397 from JoshRosen/refactoring/daemon-threads

Refactor daemon thread creation
Merge remote-tracking branch 'stephenh/cleanup'

Conflicts:
	core/src/main/scala/spark/scheduler/local/LocalScheduler.scala
Eliminate CacheTracker.

Replaces DAGScheduler's queries of CacheTracker with BlockManagerMaster
queries.

Adds CacheManager to locally coordinate computation of cached RDDs.
Add test for driver hanging on exit (SPARK-530).
Modified BlockManagerId API to ensure zero duplicate objects. Fixed BlockManagerId testcase in BlockManagerTestSuite.
Merge pull request #405 from JoshRosen/spark-530

Add test for driver hanging on exit (SPARK-530)