add mask operation to Graph
add filter operation to GraphOps
add a predicate to GraphLab to indicate active vertices at start
vertex should be inactive if no vertices scatter to it
wip delta join.
In static Pregel, replicate only changed vertices
Test Graph.deltaJoinVertices and VertexRDD.diff
Revert changes to project/SparkBuild.scala

Changes were made in 3fc4534d19a7abf7dcb6c9ebe17e5e29f1febbc5
Re-roll last iteration of static Pregel loop
Use mask for dynamic Pregel
Merge branch 'pregel-replicate-changed' of github.com:ankurdave/graphx into pregel-replicate-changed
Test prevVTableReplicated code path
Simplify GraphImpl.deltaJoinVertices
Merge branch 'pregel-replicate-changed' of github.com:ankurdave/graphx into pregel-replicate-changed
Fixed a bug in VTableReplicated that we are always broadcasting all the vertices.
Minor update.
Fixed a bug in VTableReplicated that we only process the first block.
Merge pull request #90 from amplab/pregel-replicate-changed

Replicate only changed vertices
Set RDD names for easy debugging
Merge pull request #92 from ankurdave/rdd-names

Set RDD names for easy debugging