This fixes ticket #167

Dumping boost::adjacency_list<> improves memory usage by a factor of
two, and also slightly improves performance in some cases.

This adds a check for directed graphs in most functions of the flow
module, and renames the kolmogorov_max_flow to
koybov_kolmogorov_max_flow.

This also optimizes the graph augmentation in
koybov_kolmogorov_max_flow, where reversed edges are detected and used
if they exist.

Now, whenever GraphWrap is being used, the property maps are always
in "checked" mode.

This includes the edmonds karp, push relabel and kolmogorov maximum flow
algorithms from the BGL.