#108 dead connections should time out

[Jason Dorje Short]

Currently, if a connection to a client dies it can stay
open as long as TCP will let it. This can be an
unacceptably long time.

One suggestion is that ggzd should automatically cut a
connection if it exceeds a certain lag time; say 2
minutes. This would be a two-linee change, I think.
However, this could (though it usually would not!)
erronously cut connections to players whose TCP
connections were still alive.

Another idea is to leave the connection open, *so long
as that player doesn't try to log in again*. But if
jdorje has a sufficiently high lag and someone else
(i.e. me) *correctly* tries to log in as jdorje, ggzd
should cut the original connection to jdorje and
immediately allow the new login. This, unfortunately,
would take a little bit more code (but still not very
much).