check and install disk image

tools/boot/sarge/boot-i386

@@ -159,10 +159,12 @@ EOF
 # Only disk one gets the extra files installed
 if [ "$NN" = "1" ]; then
 	# populate the install directory as well
-	for disk in $DISK_IMAGES; do
+	for disk in $DISK_IMAGES $EXTRA_DISK_IMAGES; do
+          if [ -e "$disk" ]; then
 		dir=$(dirname $disk)
 		mkdir -p $CDDIR/install/$dir
 		cp -lf $disk $CDDIR/install/$dir
+          fi
 	done
 
 	# Include Smart Boot Manager image for people where isolinux fails