Update comments in util_filter.h about bucket and brigade ownership to reflect

current practice and the advice from manual/developer/output-filters.xml.

Submitted by: Rici Lake <rici ricilake.net>
Reviewed by: Stefan Fritsch, Joe Orton


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@822870 13f79535-47bb-0310-9956-ffa450edef68