(nslookup-mode): Now implemented as a derived mode.
(ftp-mode): Now implemented as a derived mode.
(dig): Added this function.
(dig-program): Added this variable.
(network-service-connection): Likewise.
(whois-server-name): Defaults to whois.arin.net
(whois-server-list, whois-server-tld, whois-guess-server): New var.
(whois): Tries to guess the appropriate top-level domain server.
(whois-get-tld): New function.