status: advertise --abort instead of 'update -C .' to abort a merge

status has a part where it shows the conflict information and how to continue or
abort. Couple of release ago, we got merge --abort and we should advertise that
instead of 'hg update -C .' which is kind of ugly.

I know we need to unify the logic here.

Differential Revision: https://phab.mercurial-scm.org/D4168

mercurial/cmdutil.py

@@ -617,7 +617,7 b' def _graftmsg():'
 
 def _mergemsg():
     # tweakdefaults requires `update` to have a rev hence the `.`
-     return _helpmessage('hg commit', _updatecleanmsg())
+     return _helpmessage('hg commit', 'hg merge --abort')
 
 def _bisectmsg():
     msg = _('To mark the changeset good:    hg bisect --good\n'

tests/test-conflict.t

@@ -58,7 +58,7 b''
   # To mark files as resolved:  hg resolve --mark FILE
   
   # To continue:    hg commit
-  # To abort:       hg update --clean . (warning: this will discard uncommitted changes)
+  # To abort:       hg merge --abort
   
 
   $ cat a