GraphvizAlgorithm.WriteEdges(..) does not differ between directed and undirected edges

[DavidHollman]

I noticed this problem today but then found that it already had been reported here:
https://quickgraph.codeplex.com/workitem/25880

The summary is:

If I export an undirectedgraph into graphviz, the edges will appear in the dot file as:
Vertex1 -> Vertex2
But because of the graph is undirected the output should look like:
Vertex1 -- Vertex2

Because of this the GraphViz dot program will actually throw an error. For the time being I am manually replacing the -> with -- using a string replace before writing to the .dot file.

Thanks