[luatex] luatexbase.add_to_callback does not preserve the order

[David Carlisle]

Hm, yes I can reproduce here, some values the list gets reconstructed
as it was, some it re-orders: which sounds like misusing a hash
somewhere. I'll look later but I have added a simplified case that
just removes and replaces one function as an issue in github

https://github.com/josephwright/ltluatexsupp/issues/6

Thanks for the clear test file!

David