def git_commit(name, repository, branch_name = None):
"""Return the a Commit object if 'name' is a patch name or Git commit.
The patch names allowed are in the form '<branch>:<patch>' and can
- be followed by standard symbols used by git-rev-parse. If <patch>
+ be followed by standard symbols used by git rev-parse. If <patch>
is '{base}', it represents the bottom of the stack.
"""
# Try a [branch:]patch name first