Make the proxy work with filters. We are still using BUFF for the

Make the proxy work with filters.  We are still using BUFF for the
back-end communication, but BUFF has been removed from the communication
with the client.  The headers are not working correctly yet, but we are
making progress.  The most important part of this commit is that we are
able to actually filter data coming from the proxy.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86978 13f79535-47bb-0310-9956-ffa450edef68