Update documentation to match prototype for ap_register_input_filter and

ap_register_output_filter.

Submitted by: Stas Bekman <stas@stason.org>,
              Joe Schaefer <joe+apache@sunstarsys.com>
Reviewed by: Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@98244 13f79535-47bb-0310-9956-ffa450edef68