Make Caching work for subrequests.

If this is not set to one under the AP_FTYPE_CONTENT_SET
then the EOS is eaten by the CORE_SUBREQ (name?) filter
causing us not to cache anything


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@96499 13f79535-47bb-0310-9956-ffa450edef68