Fixed #15207 -- Added versionadded directives for the "using" argument sent by signals, and cleaned up some incidental indentation/formatting inconsistencies. Thanks to Keryn Knight for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15443 bcc190cf-cafb-0310-a4f2-bffc1f526a37