Arrange that we really _can_ compile all the puzzles into a single

binary if we choose: fix bugs in cube.c and sixteen.c that manifest
when compiled that way, and introduce list.c which provides a global
list of all the available puzzles.

[originally from svn r5169]

sixteen.c

@@ -769,6 +769,10 @@ static int game_wants_statusbar(void)
     return TRUE;
 }
 
+#ifdef COMBINED
+#define thegame sixteen
+#endif
+
 const struct game thegame = {
     "Sixteen", "games.sixteen", TRUE,
     default_params,