summary: print unstable, bumped and divergent as unconditionally plural

This aligns with the unconditional plural output for the update line contents,
as well as the incoming/outgoing bookmarks line.  It also matches the message
in evolve's summary hook as of 4f83b2d2d20d.  (Though I thought this was removed
recently?)

mercurial/commands.py

@@ -6538,9 +6538,9 b' def summary(ui, repo, **opts):'
             numtrouble = len(repo.revs(trouble + "()"))
             # We write all the possibilities to ease translation
             troublemsg = {
-               "unstable": _("unstable: %d changeset"),
-               "divergent": _("divergent: %d changeset"),
-               "bumped": _("bumped: %d changeset"),
+               "unstable": _("unstable: %d changesets"),
+               "divergent": _("divergent: %d changesets"),
+               "bumped": _("bumped: %d changesets"),
             }
             if numtrouble > 0:
                 ui.status(troublemsg[trouble] % numtrouble + "\n")

tests/test-obsolete.t

@@ -245,7 +245,7 b' We need to create a clone of 5 and add a'
   commit: (clean)
   update: 1 new changesets, 2 branch heads (merge)
   phases: 1 draft
-  bumped: 1 changeset
+  bumped: 1 changesets
   $ hg up '5^'
   0 files updated, 0 files merged, 1 files removed, 0 files unresolved
   $ hg revert -ar 5
@@ -480,7 +480,7 b' detect outgoing obsolete and unstable'
   commit: (clean)
   update: 1 new changesets, 2 branch heads (merge)
   phases: 3 draft
-  unstable: 1 changeset
+  unstable: 1 changesets
   $ hg log -G -r '::unstable()'
   @  5:cda648ca50f5 (draft) [tip ] add original_e
   |