[SPARK-6510][GraphX]: Add Graph#minus method to act as Set#difference

Adds a `Graph#minus` method which will return only unique `VertexId`'s from the calling `VertexRDD`.

To demonstrate a basic example with pseudocode:

```
Set((0L,0),(1L,1)).minus(Set((1L,1),(2L,2)))
> Set((0L,0))
```

Author: Brennon York <brennon.york@capitalone.com>

Closes #5175 from brennonyork/SPARK-6510 and squashes the following commits:

248d5c8 [Brennon York] added minus(VertexRDD[VD]) method to avoid createUsingIndex and updated the mask operations to simplify with andNot call
3fb7cce [Brennon York] updated graphx doc to reflect the addition of minus method
6575d92 [Brennon York] updated mima exclude
aaa030b [Brennon York] completed graph#minus functionality
7227c0f [Brennon York] beginning work on minus functionality

1 files changed, 2 insertions, 0 deletions

diff --git a/docs/graphx-programming-guide.md b/docs/graphx-programming-guide.md
index c601d793a2..3f10cb2dc3 100644
--- a/docs/graphx-programming-guide.md
+++ b/docs/graphx-programming-guide.md
@@ -899,6 +899,8 @@ class VertexRDD[VD] extends RDD[(VertexID, VD)] {
   // Transform the values without changing the ids (preserves the internal index)
   def mapValues[VD2](map: VD => VD2): VertexRDD[VD2]
   def mapValues[VD2](map: (VertexId, VD) => VD2): VertexRDD[VD2]
+  // Show only vertices unique to this set based on their VertexId's
+  def minus(other: RDD[(VertexId, VD)])
   // Remove vertices from this set that appear in the other set
   def diff(other: VertexRDD[VD]): VertexRDD[VD]
   // Join operators that take advantage of the internal indexing to accelerate joins (substantially)