Mercurial backend list_directory returns nothing

[clsdaniel]

This happens when you give list_directory a path which does not end with a slash, this is contrary to the behavior of all other backends and is a easy one, just check for the trailing slash and added when needed.

I already have a commit for this:
http://github.com/clsdaniel/pyvcs/commit/eb8e8d263718dd077d43e75a67ccdc1f54c9801a