'Process a ResetCommand.'

def reset_handler(self, cmd):

    if (cmd.from_ is None):
        from_ = ZERO_SHA
    else:
        from_ = cmd.from_
        if from_.startswith(':'):
            from_ = self.markers[from_[1:]]
    self._reset_base(from_)
    self.repo.refs[cmd.ref] = from_
