new directive 'ProxyPreserveHost' which allows the incoming host line to

be sent to the proxied server.

Submitted by:	g.russell@ieee.org (1.3 version)
Reviewed by:	Ian Holsman/Graham Legget/Chuck Murcko


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93089 13f79535-47bb-0310-9956-ffa450edef68