[tlbuild] casefolding fallback search

[Karl Berry]

Hello builders,

Jonathan committed a bunch of xetex fixes yesterday.

And I committed some changes to kpathsea/pathsearch.c to partially
implement a fallback casefolding search. It should only be compiled in
on Unix; #ifdef-d out on Windows.

I don't know of anything else major that we're waiting for (?), so it
seems like a decent time to do another test build.  If it goes ok, maybe
we can move the schedule up ...

As far as the casefolding hack goes, I expect that bugs remain. It can
be tested with kpsewhich --casefold, and any and all testing is
welcome. Probably easiest to move the kpsewhich binary into the bindir
so it finds texmf.cnf, etc.

It's "partial" because I only did the casefolding in actual directories
that are searched (like .), not the database-only trees like texmf-dist
and texmf-local. I'm not convinced case-insensitive matching in the big
trees is all that useful, and it's essentially twice the work.

I drafted a couple sections for the kpathsea manual about it, see
kpathsea.texi or kpathsea.info.  It's annoyingly long and boring, but I
felt the need to explain, especially since compatibility is not perfect
-- I think it will be sufficient, but this is one of the things I want
feedback on.

My current thought is to enable this by default, because if
compatibility is ok, the only effect should be to reduce annoyance in
working on cross-platform documents. If there are opinions otherwise,
or any other comments or criticisms, of course let me know.

I'll write the main list about it soon.

--thanks, karl.