Merge r483633 from trunk:

* Do not replace a Date header set by a proxied backend server.

PR: 40232

Submitted by: rpluem
Reviewed by: rpluem, jim, niq 


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@572272 13f79535-47bb-0310-9956-ffa450edef68