commitextras: fix on Python 3 by using sysstrs for __dict__ ops

I'm dubious of the __dict__ shenanigans in use here, but lack the
enthusiasm for figuring out why that was done right now.

# skip-blame just some r prefixes

Differential Revision: https://phab.mercurial-scm.org/D2435

hgext/commitextras.py

@@ -1,76 +1,76 b''
 # commitextras.py
 #
 # Copyright 2013 Facebook, Inc.
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 '''adds a new flag extras to commit (ADVANCED)'''
 
 from __future__ import absolute_import
 
 import re
 
 from mercurial.i18n import _
 from mercurial import (
     commands,
     error,
     extensions,
     registrar,
 )
 
 cmdtable = {}
 command = registrar.command(cmdtable)
 testedwith = 'ships-with-hg-core'
 
 usedinternally = {
     'amend_source',
     'branch',
     'close',
     'histedit_source',
     'topic',
     'rebase_source',
     'intermediate-source',
     '__touch-noise__',
     'source',
     'transplant_source',
 }
 
 def extsetup(ui):
     entry = extensions.wrapcommand(commands.table, 'commit', _commit)
     options = entry[1]
     options.append(('', 'extra', [],
         _('set a changeset\'s extra values'), _("KEY=VALUE")))
 
 def _commit(orig, ui, repo, *pats, **opts):
     origcommit = repo.commit
     try:
         def _wrappedcommit(*innerpats, **inneropts):
             extras = opts.get(r'extra')
             if extras:
                 for raw in extras:
                     if '=' not in raw:
                         msg = _("unable to parse '%s', should follow "
                                 "KEY=VALUE format")
                         raise error.Abort(msg % raw)
                     k, v = raw.split('=', 1)
                     if not k:
                         msg = _("unable to parse '%s', keys can't be empty")
                         raise error.Abort(msg % raw)
                     if re.search('[^\w-]', k):
                         msg = _("keys can only contain ascii letters, digits,"
                                 " '_' and '-'")
                         raise error.Abort(msg)
                     if k in usedinternally:
                         msg = _("key '%s' is used internally, can't be set "
                                 "manually")
                         raise error.Abort(msg % k)
                     inneropts[r'extra'][k] = v
             return origcommit(*innerpats, **inneropts)
 
         # This __dict__ logic is needed because the normal
         # extension.wrapfunction doesn't seem to work.
-        repo.__dict__['commit'] = _wrappedcommit
+        repo.__dict__[r'commit'] = _wrappedcommit
         return orig(ui, repo, *pats, **opts)
     finally:
-        del repo.__dict__['commit']
+        del repo.__dict__[r'commit']