'Send a UIDL command to retrieve the UIDs of all messages on the server.
@type consumer: L{None} or callable that takes
2-L{tuple} of (0) L{int}, (1) L{bytes}
@param consumer: A function which consumes the 0-based message index
and UID derived from the server response.
@rtype: L{Deferred <defer.Deferred>} which fires with L{list} of
L{object} or callable that takes 2-L{tuple} of (0) L{int},
(1) L{bytes}
@return: A deferred which fires when the entire response has been
received.  When a consumer is not provided, the return value is a
list of message sizes.  Otherwise, it returns the consumer itself.'

def listUID(self, consumer=None):

    return self._consumeOrSetItem('UIDL', None, consumer, _uidXform)
