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.h

@@ -45,6 +45,11 @@
 			extern "C" {
 		#endif
 
+	/* Preprocessor Checks: */
+		#if !defined(__INCLUDE_FROM_USB_DRIVER)
+			#error Do not include this file directly. Include LUFA/Drivers/USB.h instead.
+		#endif
+		
 	/* Private Interface - For use in library only: */
 	#if !defined(__DOXYGEN__)
 		/* Macros: */