A total hack for removing shuffle files

Conflicts:

	core/src/main/scala/org/apache/spark/storage/StoragePerfTester.scala

Conflicts:

	core/src/main/scala/org/apache/spark/storage/BlockManager.scala
	core/src/main/scala/org/apache/spark/storage/ShuffleBlockManager.scala
	core/src/main/scala/spark/storage/StoragePerfTester.scala