vcs_base: Adding get_branches function and documentation.
git: Adding implementation and tests for get_branches.
hg: Implemented and tested get_branches, hg branches are weird...
bzr: NotImplementedError for get_branches, I don't know how to do this in bzr
svn: Implemented and tested the get_branches function.
code style
fix missing abstraction
svn util function to check for canonical parts of url
fix get_branches svn
by default pull remote branches on get_branch
better comment on bzr