(svn r1479) -Added highscore chart (accessible from the difficulty window) with top5 companies for a given difficulty (select the difficulty in the menu)

-Added endgame score on 1 jan 2051 where you are added to the highscore if sufficiently large points have been accumulated. Game is paused while
-These values are saved in hs.dat; added read/write functions for it
-Added code to delete all windows to show charts. There is one issue left: somehow a news-gui pops up in front of the the chart at the end of the game.

ttd.c

@@ -648,6 +648,7 @@ int ttd_main(int argc, char* argv[])
 #endif
 
 	LoadFromConfig();
+	LoadFromHighScore();
 
 	// override config?
 	if (musicdriver[0]) ttd_strlcpy(_ini_musicdriver, musicdriver, sizeof(_ini_musicdriver));
@@ -748,6 +749,7 @@ int ttd_main(int argc, char* argv[])
 	_sound_driver->stop();
 
 	SaveToConfig();
+	SaveToHighScore();
 
 	// uninitialize airport state machines
 	UnInitializeAirports();
@@ -1176,9 +1178,11 @@ void BeforeSaveGame()
 {
 	Window *w = FindWindowById(WC_MAIN_WINDOW, 0);
 
-	_saved_scrollpos_x = WP(w,vp_d).scrollpos_x;
-	_saved_scrollpos_y = WP(w,vp_d).scrollpos_y;
-	_saved_scrollpos_zoom = w->viewport->zoom;
+	if (w != NULL) {
+		_saved_scrollpos_x = WP(w,vp_d).scrollpos_x;
+		_saved_scrollpos_y = WP(w,vp_d).scrollpos_y;
+		_saved_scrollpos_zoom = w->viewport->zoom;
+	}
 }
 
 void ConvertTownOwner()