Backport r239420 and r239421 to the 2.2.x branch; Enhance
CacheEnable/CacheDisable to be of use to proxy servers.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@290133 13f79535-47bb-0310-9956-ffa450edef68