update: for "noconflict" updates, print "conflicting changes" on conflict

With experimental.updatecheck=noconflict, if the update is aborted
because of conlicts, "uncommitted changes" is not quite
accurate. Let's use "conflicting changes" instead. Also fix the hint
to recomment --clean, not --merge, since that's what we do for other
failed updates.

mercurial/merge.py

@@ -1602,8 +1602,8 b' def update(repo, node, branchmerge, forc'
         if updatecheck == 'noconflict':
             for f, (m, args, msg) in actionbyfile.iteritems():
                 if m not in ('g', 'k', 'r'):
-                    msg = _("uncommitted changes")
-                    hint = _("commit or update --merge to allow merge")
+                    msg = _("conflicting changes")
+                    hint = _("commit or update --clean to discard changes")
                     raise error.Abort(msg, hint=hint)
 
         # Prompt and create actions. Most of this is in the resolve phase

tests/test-update-branches.t

@@ -295,8 +295,8 b' File conflict is not allowed'
   $ hg up -qC 3
   $ echo dirty >> a
   $ hg up -q 4
-  abort: uncommitted changes
-  (commit or update --merge to allow merge)
+  abort: conflicting changes
+  (commit or update --clean to discard changes)
   [255]
   $ hg up -m 4
   merging a