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.

hgext/mq.py

@@ -929,11 +929,11 b' class queue(object):'
         self._cleanup(realpatches, numrevs, opts.get('keep'))
 
     def checktoppatch(self, repo):
+        '''check that working directory is at qtip'''
         if self.applied:
             top = self.applied[-1].node
             patch = self.applied[-1].name
-            pp = repo.dirstate.parents()
-            if top not in pp:
+            if repo.dirstate.p1() != top:
                 raise util.Abort(_("working directory revision is not qtip"))
             return top, patch
         return None, None