(svn r5714) Backport from branches/TGP (r5701 and r5711)

-Fix: < > boxes in patch-settings didn't grey out when they hit the limit of their range
 -Codechange: while at it, prettyfied DrawArrowButtons() a bit
 -Fix: < > boxes in industry production window (when cheat enabled) had a minor glitch

gui.h

@@ -17,7 +17,7 @@ void ShowGameOptions(void);
 void ShowGameDifficulty(void);
 void ShowPatchesSelection(void);
 void ShowNewgrf(void);
-void DrawArrowButtons(int x, int y, int ctab, byte state, bool enabled);
+void DrawArrowButtons(int x, int y, int ctab, byte state, bool clickable_left, bool clickable_right);
 
 /* graph_gui.c */
 void ShowOperatingProfitGraph(void);