The database cache wasn't correctly handling expired keys. Fixed now.
The database cache wasn't correctly handling expired keys. Fixed now.

The cache tests have been failing for a long time with the db backend. This
change makes them pass again, so no test changes required here.

git-svn-id: 554f83ef17aa7291f84efa897c1acfc5d0035373@9942 bcc190cf-cafb-0310-a4f2-bffc1f526a37

svn2github/django,svn2github/django,svn2github/django