Initial Filtering code. This uses a bucket brigade scheme to allow modules

to add and modify data while processing a request.  The docs still need
to be updated, and a simple html page needs to be created explaining all
of this.

The only filter currently in the code is the core filter.  This filter
takes a bucket brigade and writes it to the network through the buff
structure.  In time, the buff will go away completely.

More filters will need to be written.
Submitted by:	The Apache Community
Reviewed by:	The Apache Community


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86059 13f79535-47bb-0310-9956-ffa450edef68