Added the fine grained backlight hierarchy code.

Depending on how the server sets the backlight it controls the clients
(if OPEN then the clients have individual control). If the client is set to
open (inherited from the server) then each screen has backlight control.

server/screen.h

@@ -12,6 +12,7 @@ typedef struct screen {
 	int duration;
 	int heartbeat;
 	int timeout;
+	int backlight_state;
 	char *keys;
 	LinkedList *widgets;
 	client *parent;