(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.

functions.h

@@ -233,6 +233,7 @@ void LoadFromConfig(void);
 void SaveToConfig(void);
 void CheckConfig(void);
 int ttd_main(int argc, char* argv[]);
+void HandleExitGameRequest(void);
 
 void DeterminePaths(void);