def list_directory(self, path, revision=None, branch=None):
        raise NotImplementedError
Used by actor (owner) to check number of tokens on the port.
dataset/ETHPy150Open washingtontimes/django-repositories/repositories/vcs/base.py/BaseVCS.list_directory--crossover with--dataset/ETHPy150Open EricssonResearch/calvin-base/calvin/actor/actorport.py/InPort.available_tokens