Create different backends for different vcs (bzr,git, hg, svn, etc)

Currently there is only support for bazaar inside filezaar, I would like to add support for other version control systems such as git, hg or svn
for git:
research:
Dulwich: http://samba.org/~jelmer/dulwich/ (implementation on Git purely written in python)
Git-python: http://gitorious.org/git-python (Python bindings for GIT)