mod_cache: Make option "CacheDisable" in mod_cache case insensitive PR 54462

trunk patch: http://svn.apache.org/r1464721
Submitted by: Tianyin Xu <tixu cs ucsd edu>
Reviewed by: jailletc36, fuankg, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1490581 13f79535-47bb-0310-9956-ffa450edef68