mod_disk_cache: Decline the opportunity to cache if the response is

a 206 Partial Content. This stops a reverse proxied partial response
from becoming cached, and then being served in subsequent responses.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@951222 13f79535-47bb-0310-9956-ffa450edef68