(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.h

@@ -449,6 +449,7 @@ enum {
 	WC_NETWORK_STATUS_WINDOW = 0x4A,
 	WC_CUSTOM_CURRENCY = 0x4B,
 	WC_REPLACE_VEHICLE = 0x4C,
+	WC_HIGHSCORE_ENDSCREEN = 0x4D,
 };