Fixed #15092 -- Made `{% now %}` work with single-quoted string arguments....

Fixed #15092 -- Made `{% now %}` work with single-quoted string arguments. Thanks to ninja_otoko for the report and to steveire, Aymeric Augustin and Claude Paroz for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17391 bcc190cf-cafb-0310-a4f2-bffc1f526a37