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/HighLevel/USBInterrupt.c

@@ -28,6 +28,7 @@
   this software.
 */
 
+#define  __INCLUDE_FROM_USB_DRIVER
 #include "USBInterrupt.h"
 
 void USB_INT_DisableAllInterrupts(void)