Add more include protection macros to give the user warnings when they try to manually include private driver header files, instead of the public driver headers.

LUFA/Drivers/USB/Class/Printer.h

@@ -51,6 +51,10 @@
 #ifndef _PRINTER_CLASS_H_
 #define _PRINTER_CLASS_H_
 
+	/* Macros: */
+		#define __INCLUDE_FROM_PRINTER_DRIVER
+		#define __INCLUDE_FROM_USB_DRIVER
+
 	/* Includes: */
 		#include "../HighLevel/USBMode.h"