Backporting the following fix from 2.1-dev:

  *) Modified the cache code to be header-location agnostic. Also
     fixed a number of other cache code bugs related to PR 15852.
     Includes a patch submitted by Sushma Rai <rsushma novell.com>.
     This fixes mod_mem_cache but not mod_disk_cache yet so I'm not
     closing the PR since that is what they are using.
     Reviewed by: Fielding, Trawick


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@102015 13f79535-47bb-0310-9956-ffa450edef68