Modify buff.h and buff.c to enable modules to intercept the

output byte stream for dynamic page caching. A pointer to a
'filter callback' function is added to the end of buff.h.
This function, if registered by a module, is called
at the top of buff_write() and writev_it_all().

MMN Minor bumped.

Obtained from: [Kevin Mallory <kmallory@spidercache.com>
Reviewed by:	Bill Stoddard


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@92260 13f79535-47bb-0310-9956-ffa450edef68