Added consistent support for double- and single-quote delimiters in templates.

Some template filters and tags understood single-quoted arguments, others
didn't. This makes everything consistent. Based on a patch from akaihola.

Fixed #7295.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10118 bcc190cf-cafb-0310-a4f2-bffc1f526a37