Added preprocessor checks and documentation to the bootloaders giving information about missing SIGNATURE_x defines due to outdated avr-libc versions.

Bootloaders/DFU/BootloaderDFU.h

@@ -48,7 +48,12 @@
 		#include "Descriptors.h"
 		
 		#include <LUFA/Drivers/USB/USB.h>                // USB Functionality
-		
+	
+	/* Preprocessor Checks: */
+		#if !defined(SIGNATURE_0) || !defined(SIGNATURE_1) || !defined(SIGNATURE_2)
+			#error Device signature byte constants are not defined due to outdated avr-libc version. See demo documentation.
+		#endif
+	
 	/* Macros: */
 		/** Configuration define. Define this token to true to case the bootloader to reject all memory commands
 		 *  until a memory erase has been performed. When used in conjunction with the lockbits of the AVR, this

Bootloaders/DFU/BootloaderDFU.txt

@@ -73,5 +73,12 @@
  *        erase has been perfomed. This can be used in conjunction with the AVR's lockbits to prevent the AVRs firmware from
  *        being dumped by unauthorized persons.</td>
  *   </tr>
+ *   <tr>
+ *    <td>SIGNATURE_0, SIGNATURE_1, SIGNATURE_2</td>
+ *    <td>Makefile CDEFS</td>
+ *    <td>AVR part signature bytes. These are normally defined as part of the AVR device header files in recent avr-libc
+ *        distributions. If your avr-libc library is out of date and does not define these values, you can define them
+ *        manually in the makefile CDEFS.</td>
+ *   </tr>
  *  </table>
  */