def connect(host, port = FTP_PORT)
      if @debug_mode
        print "connect: ", host, ", ", port, "\n"
      end
      synchronize do
        @sock = open_socket(host, port)
        voidresp
      end
    end
Establishes an FTP connection to host, optionally overriding the default
port. If the environment variable +SOCKS_SERVER+ is set, sets up the
connection through a SOCKS proxy. Raises an exception (typically
<tt>Errno::ECONNREFUSED</tt>) if the connection cannot be established.