The core filter should not be using its own brigade inside its own ctx

structure.  This changes the core_output_filter to use a brigade inside
the conn_rec.  Think of this as analagous to the BUFF in the conn_rec.
The idea is that if we have pipelined requests, and it isn't worth it to
send the last bit of data from the first request, we want to save that
extra bit of data to the conn_rec, so that the next request sends it
automatically.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86433 13f79535-47bb-0310-9956-ffa450edef68