mq: checktoppatch should only check if p1 is qtip
There is no way qtip in p2 could be used for anything, and there is thus no
reason to check and accept it.
mq: fix qpop of working directory parent patch when not at qtip
mq assumed that it had to update from qtip to qparent, and instead of updating
from where it was it failed with:
abort: working directory revision is not qtip