I added numeric_owner to the self.chown() call when adding directories. I'm reasonably sure this is correct.

I added tests for dirs, although they need some cleaning up to be simpler and cleaner. I'll do that cleanup shortly, but I want to check this in before I get on a plane.

I also changed the tests to use different numbers for .gid and .uid, in order to pick up if there's a transposition error somewhere.

If anyone can test this on Windows, that would be helpful.