Fixed #22127 -- Reverse default ordering in Trac's ticket list

https://code.djangoproject.com/ticket/22127

As trac is rather a behemoth to install, I have not tested this patch myself. However, based on http://trac.edgewall.org/changeset/7553 and http://trac.edgewall.org/wiki/TicketQuery, this should be the correct change.