Update the patch for environment variable interpolation in

ProxyPass/Reverse/etc directives: r421686, r422178, r421686, r421725
That patch stalled on wrowe's veto.  This update introduces a new
"interpolate" keyword to all directives affected, so should meet
his concerns by adding explicit per-directive control (disabled
by default).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@589371 13f79535-47bb-0310-9956-ffa450edef68