Fixed #12980 - Use raw strings for locale formats which contain single...

Fixed #12980 - Use raw strings for locale formats which contain single backslahes. Thanks for report and patch, Martin von Löwis and Ramiro Morales.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13050 bcc190cf-cafb-0310-a4f2-bffc1f526a37