Merge pull request #147 from mosharaf/dev

core/src/main/scala/spark/SparkContext.scala

core/src/main/scala/spark/SparkEnv.scala

.../src/main/scala/spark/broadcast/BitTorrentBroadcast.scala

core/src/main/scala/spark/broadcast/Broadcast.scala

core/src/main/scala/spark/broadcast/BroadcastFactory.scala

core/src/main/scala/spark/broadcast/ChainedBroadcast.scala

core/src/main/scala/spark/broadcast/DfsBroadcast.scala

core/src/main/scala/spark/broadcast/HttpBroadcast.scala

core/src/main/scala/spark/broadcast/MultiTracker.scala

core/src/main/scala/spark/broadcast/SourceInfo.scala

core/src/main/scala/spark/broadcast/TreeBroadcast.scala

core/src/main/scala/spark/executor/Executor.scala