(nntp-netcat-command): Rename from nntp-via-netcat-command.

(nntp-netcat-command): Rename from nntp-via-netcat-command.
(nntp-netcat-switches): Rename from nntp-via-netcat-switches.
(nntp-open-telnet, nntp-open-rlogin): Use with-current-buffer.
(nntp-service-to-port): New function.
(nntp-open-via-rlogin-and-netcat, nntp-open-via-telnet-and-telnet)
(nntp-open-telnet-stream, nntp-open-via-rlogin-and-telnet): Use it.
(nntp-open-netcat-stream): New function.
(nntp-open-via-rlogin-and-netcat): Don't use a pty.