Fixed #14231 -- Added an index to the expire_date column on the Session model....

Fixed #14231 -- Added an index to the expire_date column on the Session model. Thanks to joeri for the report, via Frodo from Medid.

This won't affect any existing session tables; see the release notes for migration instructions.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14378 bcc190cf-cafb-0310-a4f2-bffc1f526a37