def get_refs(self, location):
        """Return map of named refs (branches or tags) to commit hashes."""
        output = call_subprocess([self.cmd, 'show-ref'],
                                 show_stdout=False, cwd=location)
        rv = {}
        for line in output.strip().splitlines():
            commit, ref = line.split(' ', 1)
            ref = ref.strip()
            ref_name = None
            if ref.startswith('refs/remotes/'):
                ref_name = ref[len('refs/remotes/'):]
            elif ref.startswith('refs/heads/'):
                ref_name = ref[len('refs/heads/'):]
            elif ref.startswith('refs/tags/'):
                ref_name = ref[len('refs/tags/'):]
            if ref_name is not None:
                rv[ref_name] = commit.strip()
        return rv
Return map of named refs (branches or tags) to commit hashes.