backport from head:

mod_disk_cache: don't store hop-by-hop headers on-disk.

Submitted by:	Justin Erenkrantz
Reviewed by:	Cliff Woolley, Jeff Trawick


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@105371 13f79535-47bb-0310-9956-ffa450edef68