Fixed #10447 -- Made sure the syndication feeds helper function that returns...

Fixed #10447 -- Made sure the syndication feeds helper function that returns RFC 2822-formatted datetime strings isn't affected by the current locale, removing use of strftime() because the '%a' and '%b' format specifiers are problematic in this respect. Thanks bear330 for the report and lupus for an initial patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15112 bcc190cf-cafb-0310-a4f2-bffc1f526a37