Fault tolerance and block store fixes discovered through streaming tests.

core/src/main/scala/spark/BlockStoreShuffleFetcher.scala

core/src/main/scala/spark/MapOutputTracker.scala

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

core/src/main/scala/spark/network/Connection.scala

core/src/main/scala/spark/network/ConnectionManager.scala

core/src/main/scala/spark/scheduler/ShuffleMapTask.scala

.../spark/scheduler/cluster/StandaloneSchedulerBackend.scala

core/src/main/scala/spark/scheduler/cluster/TaskInfo.scala

...c/main/scala/spark/scheduler/cluster/TaskSetManager.scala

core/src/main/scala/spark/storage/BlockManager.scala