Added xxx_Unregister() functions to all common controls.

diff --git a/include/trackbar.h b/include/trackbar.h
index ae3cf8b..9962d12 100644
--- a/include/trackbar.h
+++ b/include/trackbar.h
@@ -40,6 +40,7 @@
 
 
 
-extern void TRACKBAR_Register (void);
+extern VOID TRACKBAR_Register (VOID);
+extern VOID TRACKBAR_Unregister (VOID);
 
 #endif  /* __WINE_TRACKBAR_H */