subrepo: don't commit in subrepo if it's clean

If a subrepo has changed relative to the outer repo's substate, but the
subrepo itself is clean, we don't need to commit in the subrepo.

mercurial/subrepo.py

@@ -420,6 +420,10 b' class hgsubrepo(abstractsubrepo):'
         return self._repo._checknested(self._repo.wjoin(path))
 
     def commit(self, text, user, date):
+        # don't bother committing in the subrepo if it's only been
+        # updated
+        if not self.dirty(True):
+            return self._repo['.'].hex()
         self._repo.ui.debug("committing subrepo %s\n" % subrelpath(self))
         n = self._repo.commit(text, user, date)
         if not n:

tests/test-mq-subrepo.t

@@ -348,3 +348,14 b' handle subrepos safely on qrecord'
   % debugsub should be empty
 
   $ cd ..
+
+
+correctly handle subrepos with patch queues
+  $ mkrepo repo-subrepo-with-queue
+  $ mksubrepo sub
+  adding a
+  $ hg -R sub qnew sub0.diff
+  $ echo sub = sub >> .hgsub
+  $ hg add .hgsub
+  $ hg qnew 0.diff
+  committing subrepository sub