I can't see a way to do this after looking at liolib.c and googling a bit.
It's obviously fairly trivial to extend liolib.c to do it, but a pain as
you can't do it with vanilla Lua.
Am I missing something? I don't imagine it's that rare to want to pass a
FILE * obtained from somewhere else into a Lua script without re-inventing
the liolib wheel...