Pass a game_ui to compute_size, print_size and print.

I'm about to move some of the bodgy getenv-based options so that they
become fields in game_ui. So these functions, which could previously
access those options directly via getenv, will now need to be given a
game_ui where they can look them up.

netslide.c

@@ -1223,7 +1223,7 @@ static void game_free_drawstate(drawing *dr, game_drawstate *ds)
 }
 
 static void game_compute_size(const game_params *params, int tilesize,
-                              int *x, int *y)
+                              const game_ui *ui, int *x, int *y)
 {
     /* Ick: fake up `ds->tilesize' for macro expansion purposes */
     struct { int tilesize; } ads, *ds = &ads;