* src/gnet-private.h:
* src/mcast.c: (gnet_mcast_socket_new_full),
(gnet_mcast_socket_delete), (gnet_mcast_socket_ref),
(gnet_mcast_socket_unref), (gnet_mcast_socket_get_io_channel),
(gnet_mcast_socket_get_local_inetaddr),
(gnet_mcast_socket_join_group), (gnet_mcast_socket_leave_group),
(gnet_mcast_socket_get_ttl), (gnet_mcast_socket_set_ttl),
(gnet_mcast_socket_is_loopback), (gnet_mcast_socket_set_loopback):
* src/mcast.h:
* src/udp.c:
Move GUdpSocket structure back into gnet-private.h and make
GMcastSocket derive from it explicitly and properly. More and
better guards for input to public gnet_mcast_*() functions.