#6 randomwalk seems to only work on undirected graphs

[bh2]

when running randomwalk on a directed graph (i used the
randomnetwork modeling plugin for generating the graph)
it throws a class cast exception on line 152 of
randomwalk.java:
currentNode = (UndirectedSparseVertex)
indxr.getVertex(currentPosition[i]);

we need to see if this algorithm can support directed
graphs and if so update the randomwalk algorithm