Merge r1753228, r1753229 from trunk:

httpoxy workarounds, first draft patch as published for all 2.2.x+ sources

Optimization to httpoxy workaround, for 2.4.23+ only.

Submitted by: Dominic Scheirlinck <dominic vendhq.com>, ylavic
Reviewed/backported by: wrowe, jim, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1756559 13f79535-47bb-0310-9956-ffa450edef68