Fix directed_graph::swap
Merge branch 'develop' of github.com:boostorg/graph into develop
Add tests for member swap and fix undirected_graph<>::swap
Add tests for member swap and fix undirected_graph<>::swap
Merge pull request #5 from BenPope/develop

Fix [un]directed_graph::swap and add tests

Nice job, thanks!  I'll have to look at your other points a bit more carefully before responding.