Determine if file is known by git.

def is_git_file(cls, path, name):
        """Determine if file is known by git."""
        os.chdir(path)
        p = subprocess.Popen(['git', 'ls-files', '--error-unmatch', name],
                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        p.wait()
        return p.returncode == 0