Major rework of ap_proxy_ftp_handler() to use filters (begone foul

BUFF!!!). It compiles, but is untested, and the build environment needs
to be fixed to include proxy_ftp.c.
PR:
Obtained from:
Reviewed by:


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@88734 13f79535-47bb-0310-9956-ffa450edef68