Merge branch 'master' of github.com:amplab/graphx

core/src/main/scala/org/apache/spark/util/hash/BitSet.scala

...c/main/scala/org/apache/spark/util/hash/OpenHashMap.scala

...c/main/scala/org/apache/spark/util/hash/OpenHashSet.scala

.../org/apache/spark/util/hash/PrimitiveKeyOpenHashMap.scala

...c/test/scala/org/apache/spark/util/hash/BitSetSuite.scala

...t/scala/org/apache/spark/util/hash/OpenHashMapSuite.scala

...t/scala/org/apache/spark/util/hash/OpenHashSetSuite.scala

...apache/spark/util/hash/PrimitiveKeyOpenHashSetSuite.scala

...n/scala/org/apache/spark/graph/GraphKryoRegistrator.scala

.../src/main/scala/org/apache/spark/graph/VertexSetRDD.scala