Return Graph from aggregateNeighbors; update callers

This commit only affects the Graph API, not GraphImpl.
Implement aggregateNeighbors returning Graph
Return Graph from default aggregateNeighbors also
Move IndexedRDD and GraphSuite to org.apache.spark
Move IndexedRDDSuite to org.apache.spark
Move BytecodeUtils to the right package
Import appropriate Spark core classes
Merge pull request #2 from ankurdave/package-fixes

Package fixes (spark.graph -> org.apache.spark.graph)
After unit tests, clear port properties unconditionally
Merge pull request #3 from ankurdave/clear-port-properties-after-tests

After unit tests, clear port properties unconditionally

Also submitted to Spark upstream (mesos/spark#940)
Fix typo in aggregateNeighbors docs
Initialize sc in GraphSuite to avoid NullPointerException
Merge branch 'master' into aggregateNeighbors-returns-graph
Add a unit test for aggregateNeighbors
Merge pull request #1 from ankurdave/aggregateNeighbors-returns-graph

Return Graph from Graph.aggregateNeighbors
Added initial implementation of lognormal graph generator. Haven't tested it yet.
Added rmat graph generator
Fixed annotation import
Fixed bug in sampleLogNormal
Removed some comments