Fixed vertex_index to return local index instead of global index.

This is important when running a graph algorithm on a subgraph.


[SVN r19479]

libs/graph

@@ -1 +1 @@
-Subproject commit 9a6f00eb129562236653e959d36fdb0be97e8da3
+Subproject commit 9b195bb29972e52d49dd1550b9ec1472d2e3647a