'Returns True if this cmdset contains the given command (as
defined by command name and aliases). This allows for things
like \'if cmd in cmdset\''

def __contains__(self, othercmd):

    ret = self._contains_cache.get(othercmd)
    if (ret is None):
        ret = (othercmd in self.commands)
        self._contains_cache[othercmd] = ret
    return ret
