Added notes about the two new date format specifiers (``c`` and ``u``) added...

Added notes about the two new date format specifiers (``c`` and ``u``) added in 1.2. Thanks for the patch, Ramiro Morales.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13267 bcc190cf-cafb-0310-a4f2-bffc1f526a37