HTTP X-Forwarded-For/Z39.50 Client-IP support

HTTP X-Forwarded-For/Z39.50 Client-IP support

virt_db, multi: relays Z39.50 client-IP.
sru_z3950: converts X-Forwarded-For header to Z39.50 client-IP.
zoom: uses Client-IP or origin address (prefer Client-IP).
frontend_net: Strips tcp: from peer address (so that it is no longer
printed and stripped in zoom filter).
z3950_client: builds client-IP list - combining immediate peer address
as returned by COMSTACK and existing client-IP list (if avaiable).
The Origin only printes first X-Forwarded address.