PlayerNumber is a simple, regular data structure, and is depended on

by lower level things (eg. InputMapper).  However, concepts like
"joined players" and "human players" is a high-level, GAMESTATE
concept, and engine stuff shouldn't depend on that.  Move the
GameState-depending stuff into GameState.  Move
IsAnyPlayerUsingMemoryCard as well (and rename to HumanPlayer),
to fix MemoryCardManager dep.

stepmania/src/ScreenManager.cpp

@@ -71,6 +71,7 @@
 #include "ScreenDimensions.h"
 #include "Foreach.h"
 #include "ActorUtil.h"
+#include "GameState.h" // XXX: bad dep
 
 ScreenManager*	SCREENMAN = NULL;	// global and accessable from anywhere in our program