Proceed by pressing enter at netgame warning screen.

If there's some discrepancy between clients who are to play a game
together, a warning dialog is displayed. To acknowledge this message
and proceed, make the user press enter, not escape, which is
counter-intuitive.

This fixes #453 (thanks Alexandre-Xavier).
strife: Allow inventory items > 255.

The 'inventory' field in ticcmd structures can refer to inventory
values greater than the 8-bit range, so this needs to be transferred
over the network as at least a 16-bit value in order to avoid network
desyncs.

This fixes #454 (thanks Quasar).