Added an initial spark job to ensure worker nodes are initialized.
Fixed bug in CheckpointRDD to prevent exception when the original RDD had zero splits.
Fixed bugs in FileInputDStream and Scheduler that occasionally failed to reprocess old files after recovering from master failure. Completely modified spark.streaming.FailureTest to test multiple master failures using file input stream.
Changed scheduler and file input stream to fix bugs in the driver fault tolerance. Added MasterFailureTest to rigorously test master fault tolerance with file input stream.