[debug] Use a delimiter to break up DBG_HD() output

Reading sixteen columns of hex digits can be difficult; include a "-"
character to split the output into two groups of eight columns.

src/core/debug.c

 			printf ( "   " );
 			continue;
 		}
-		printf ( " %02x", bytes[i] );
+		printf ( "%c%02x",
+			 ( ( ( i % 16 ) == 8 ) ? '-' : ' ' ), bytes[i] );
 	}
 	printf ( " : " );
 	for ( i = offset ; i < ( offset + 16 ) ; i++ ) {