timestamp set when it's opened. Older copies with the same socket can
be tested against the cannonical copy maintained by tpool and sending
avoided when the timestamp shows the endpoint has likely changed.
Change tpool's list of sockets to a map for faster lookup, and get rid
of similar structure in udpqueue.
once UDP sockets and/or per-device (not per-game) connections come
along. Lots of changes, most not involving code flow but a couple
that did. So far two gtk games can connect and exchange moves.
Haven't tested reconnection or store-and-forward.
