[luatex] Misplaced letter

[Javier Bezos]

 > afaik arabic works ok in context (i'd have gotten complaints from users
 > otherwise) so maybe you don't enable the right features

Now it works in context, indeed (and this is the very reason I tried
to use the "fontloader=context"), but several months ago didn't.
It seems luaoftload is unmaintained (15 forks on GitHub!) and the
fix for this issue hasn't reached it.

I only want to know where the problem was, just to see if I can
do anything to improve the situation (or at least, to document
what to do). and finish the basic support for lua+babel+Arabic.

I've found a workaround based on introducing some explicit dirs at
some places, but a better solution is clearly preferable. (I've even
considered forking luaoftload, but it's a daunting task, you know).

Javier