[bug#30572] [PATCH 5/7] docker: Allow the addition of extra files into the image.

[Danny Milosavljevic]

> +                      (zero? (apply system* "tar" "-C" extra-items-dir
> +                                    "-rf" "layer.tar"
> +                                    (append %tar-determinism-options
> +                                            '("."))))))))

-C is order-sensitive.  Apparently it still doesn't cause layer.tar
to be created inside extra-items-dir (huh...), but for clarity, I'd prefer:

tar -rf layer.tar -C extra-items-dir .

Otherwise LGTM!