Tighten up the overridden-Server-header bugfix in the proxy, by

only overriding if the request is a proxy request. It has been
pointed out that the previous fix allows CGIs and modules to
override the Server header, which is change to previous behavior.
PR:
Obtained from:
Submitted by:	Graham Leggett, Joshua Slive
Reviewed by:


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@94165 13f79535-47bb-0310-9956-ffa450edef68