This fixes the cache code so that responses can be cached if they have
 an Expires header but no Etag or Last-Modified headers. PR 23130.
 Submitted by: <bjorn@exoweb.net>
 Reviewed by: Paul J. Reder


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@101231 13f79535-47bb-0310-9956-ffa450edef68