added support for random vertex cuts

graph/src/main/scala/org/apache/spark/graph/impl/GraphImpl.scala

@@ -466,6 +466,15 @@ object GraphImpl {
   }
 
 
+  /**
+   * Assign edges to an aribtrary machine corresponding to a 
+   * random vertex cut.
+   */
+  protected def randomVertexCut(src: Vid, dst: Vid, numParts: Pid): Pid = {
+    math.abs((src, dst).hashCode()) % Pid
+  }
+
+
   /**
    * @todo(crankshaw) how does this effect load balancing?
    */