moved flag for "game over" from player to game structure

moved flag for "game over" from player to game structure

This also removes asymmetric behaviour depending on players being the
"local player" or any other player in team mode (which happened if one
player dies and the other enters the exit, for example -- in one case,
the game will be treated as "game over", in the other case the game
will continue running without asking to play again).