Fixed #12362 -- Corrected Python 2.4 incompatibility with hmac constructor in...

Fixed #12362 -- Corrected Python 2.4 incompatibility with hmac constructor in contrib.messages. Thanks to Jeremy Dunck for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11814 bcc190cf-cafb-0310-a4f2-bffc1f526a37