(svn r6380) -Codechange: unify all ways to quit OTTD.

This means that in the intro menu the 'Quit' button immediatelly quits
  and the 'Quit' in the menu of the normal game and scenario editor
  immediatelly quits when the 'autosave_on_exit' patch is turned on.
  This is the same way as the OS/window manager initiated quits, like
  alt-F4 and the 'x' in the (OS/window manager drawn) title bar of OTTD.

video/win32_v.c

@@ -151,8 +151,6 @@ static void ClientSizeChanged(int w, int h)
 	}
 }
 
-extern void DoExitSave(void);
-
 #ifdef _DEBUG
 // Keep this function here..
 // It allows you to redraw the screen from within the MSVC debugger
@@ -256,14 +254,7 @@ static LRESULT CALLBACK WndProcGdi(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lP
 		}
 
 		case WM_CLOSE:
-			if (_game_mode == GM_MENU) { // do not ask to quit on the main screen
-				_exit_game = true;
-			} else if (_patches.autosave_on_exit) {
-				DoExitSave();
-				_exit_game = true;
-			} else {
-				AskExitGame();
-			}
+			HandleExitGameRequest();
 			_window_maximize = IsZoomed(_wnd.main_wnd);
 			return 0;