Fixed #12399 -- Added handling for memcache timeouts longer than 30 days....

Fixed #12399 -- Added handling for memcache timeouts longer than 30 days. Thanks to houdinihound for the report, and gciotta for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12408 bcc190cf-cafb-0310-a4f2-bffc1f526a37