def list_directory(self, path, revision=None):
        raise NotImplementedError
logfun should be function that takes disp_fun and line_buffer object
dataset/ETHPy150Open natestedman/Observatory/observatory/lib/pyvcs/repository.py/BaseRepository.list_directory--crossover with--dataset/ETHPy150Open deanhiller/databus/webapp/play1.3.x/python/Lib/site-packages/pyreadline/modes/emacs.py/EmacsMode.add_key_logger