Fixed problems with the new `network.c' code:

Fixed problems with the new `network.c' code:
- The client only uses one `addrinfo' address, so messages are not send twice.. The default IPv6 multicast address is prefered over the default IPv4 multicast address.
- `network_receive' is now interruptible by signals. It returns without error (and without data).
- Removed the (old) `Server' and `Port' options from `configfile.c' in favor of the (new) `cf_callback_socket'.