Report on push/pull if heads are merged, too, like for new heads.

Use case: If a remote repo has two heads and I _want_ to merge them, I merge
and push. Meanwhile someone else pushed on top of one of the heads. He won't
get a warning, because he doesn't create a new head, I won't notice that I
don't close a head, because I don't get a message telling me.

mercurial/localrepo.py

@@ -1550,8 +1550,8 b' class localrepository(object):'
 
         newheads = len(self.changelog.heads())
         heads = ""
-        if oldheads and newheads > oldheads:
-            heads = _(" (+%d heads)") % (newheads - oldheads)
+        if oldheads and newheads != oldheads:
+            heads = _(" (%+d heads)") % (newheads - oldheads)
 
         self.ui.status(_("added %d changesets"
                          " with %d changes to %d files%s\n")

tests/test-push-warn.out

@@ -47,4 +47,4 b' searching for changes'
 adding changesets
 adding manifests
 adding file changes
-added 1 changesets with 1 changes to 1 files
+added 1 changesets with 1 changes to 1 files (-1 heads)