Fixed #15144 -- Corrected some problems with the Cache middleware when used...

Fixed #15144 -- Corrected some problems with the Cache middleware when used with multiple cache settings. Thanks to Jim Dalton for the report, and to Jim and Joshua Ginsberg for the work on the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15285 bcc190cf-cafb-0310-a4f2-bffc1f526a37