Merge r806920 from trunk:

Return consistent error status for proxy unable to connect
PR 46971

Submitted by: niq
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@882153 13f79535-47bb-0310-9956-ffa450edef68