[1.6.x] Fixed #22827 -- clarified what each cache middleware does.
[1.6.x] Fixed #22827 -- clarified what each cache middleware does.

Thanks Keryn Knight for the report.

Backport of f9b7a0383c from master

felixjimenez/django,redhat-openstack/django,redhat-openstack/django,felixjimenez/django,django-nonrel/django,felixjimenez/django,redhat-openstack/django,redhat-openstack/django,django-nonrel/django,django-nonrel/django,felixjimenez/django,django-nonrel/django