Merge pull request #62 from dcrankshaw/partitioners

Allow user to choose a partitioner at runtime
Removed sleep from pagerank in Analytics.
Addressing bug in open hash set where getPos on a full open hash set could loop forever.
Switching collectNeighborIds to use mapReduceTriplets directly
adding test for collectNeighborIds
Modifying graph loaders to create initial vertex sets more efficiently and load undirected graphs.
Adding triangle count code
Now with style. Addressing most of Reynolds comments.
Switching mapReduceTriplets mapFunction to return iterator instead of array to allow optimizations of the returned object.
Setting the initial vertex set size to be small.
Adding comments and addressing comments.
Fixing build after merging upstream changes.
Merge pull request #74 from dcrankshaw/remove_sleep

Removed sleep from pagerank in Analytics
Added partition aware union to improve reduceByKeyAndWindow
Added partitioner aware union, modified DStream.window.
Added flag in window operation to use partition awaare union.
Merge pull request #73 from jegonzal/TriangleCount

Triangle count
Support preservesPartitioning in RDD.zipPartitions
Simplify GraphImpl internals
Merge pull request #75 from amplab/simplify

Simplify GraphImpl internals