Merge from master

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

core/src/main/scala/spark/Dependency.scala

core/src/main/scala/spark/PairRDDFunctions.scala

core/src/main/scala/spark/ShuffleFetcher.scala

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

core/src/main/scala/spark/api/java/JavaRDDLike.scala

...main/scala/spark/api/java/function/FlatMapFunction2.scala

core/src/main/scala/spark/rdd/CoGroupedRDD.scala

core/src/main/scala/spark/rdd/ShuffledRDD.scala

core/src/main/scala/spark/rdd/SubtractedRDD.scala

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

core/src/main/scala/spark/serializer/Serializer.scala

core/src/main/scala/spark/serializer/SerializerManager.scala

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

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

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

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

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

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

core/src/test/scala/spark/JavaAPISuite.java