[1.2.X] Fixed #14624 -- Updated a few outdated references to CacheMiddleware...

[1.2.X] Fixed #14624 -- Updated a few outdated references to CacheMiddleware in the transactions topic guide. Thanks to quinode for the report.

Backport of [14470] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14471 bcc190cf-cafb-0310-a4f2-bffc1f526a37