mod_cache: Add CacheIgnoreHeaders directive.

(Justin made some minor tweaks to the patch.)

PR: 30399
Submitted by:	R�diger Pl�m <r.pluem@t-online.de>
Reviewed by:	Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@105569 13f79535-47bb-0310-9956-ffa450edef68