backout: pass 'editform' argument to 'cmdutil.getcommiteditor'

This patch passes 'editform' argument according to the format below:

  COMMAND[.ROUTE]

  - ROUTE: name of route, if there are two or more routes in COMMAND

In this patch, ROUTE is omitted..

mercurial/commands.py

@@ -505,11 +505,12 b' def backout(ui, repo, node=None, rev=Non'
 
 
         def commitfunc(ui, repo, message, match, opts):
-            e = cmdutil.getcommiteditor(**opts)
+            editform = 'backout'
+            e = cmdutil.getcommiteditor(editform=editform, **opts)
             if not message:
                 # we don't translate commit messages
                 message = "Backed out changeset %s" % short(node)
-                e = cmdutil.getcommiteditor(edit=True)
+                e = cmdutil.getcommiteditor(edit=True, editform=editform)
             return repo.commit(message, opts.get('user'), opts.get('date'),
                                match, editor=e)
         newnode = cmdutil.commit(ui, repo, commitfunc, [], opts)