- route menu's CheckGame call through SysCallbacks.

Needed to be able to move the menu into the backend.

src/common/engine/i_interface.h

@@ -22,6 +22,7 @@ struct SystemCallbacks
 	void (*MenuDim)();
 	FString(*GetPlayerName)(int i);
 	bool (*DispatchEvent)(event_t* ev);
+	bool (*CheckGame)(const char* nm);
 };
 
 extern SystemCallbacks sysCallbacks;