[luatex] Allowing or switching to string indexes in Lua bytecode registers

[David Carlisle]

Thanks for that, I got some conflicts when I tried it, Also I wasn't
sure if you were testing using the existing luatexbase from ctan
(which doesn't use ltluatex code) or the version on github that does,

I suspect that we wouldn't want to overload dofile etc in the base
format (certainly not in the initial releases) however I don't see
anything in the proposed ltluatex code that would stop you making some
code along these lines into a package like the existing "mylatex" and
"mylatexformat" on ctan that overloads the latex package mechanism to
allow certain packages to be dumped into the format to at the same
time byte compile and save the package lua code.
In particular I was getting errors
attempt to index global 'luatexbase' (a nil value)
which I didn't trace completely but I think it's because the ltluatex
definition wasn't being inserted into everyjob in time
That is no doubt fixable, but I'd wait until the format code to define
luatexbase is stable and released before really testing such an
extension,

David