[Freeciv-Dev] (PR#8839) pingtime is insecure

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=8839 >

The current pingtimeout can be easily fooled by the client:

- He can make it seem higher than it is by waiting before sending the pong.

- He can make it seem lower than it is by pre-emptively sending the pong.

The former is unavoidable, but doesn't give much advantage to the 
player.  The latter is easily avoidable.  All we have to do is send a 
signature with each ping and compare it against the reply.

jason