Merge r1591143 from trunk:

mod_cache: Retry unconditional request with the full URL (including the
           query-string) when the origin server's 304 response does not
           match the conditions used to revalidate the stale entry.

http://www.mail-archive.com/dev@httpd.apache.org/msg59884.html

Submitted by: ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1595917 13f79535-47bb-0310-9956-ffa450edef68