[tex-live] web2c changes to support xetex

[Karl Berry]

    Please let me know of any concerns. Thanks.

The technical changes look fine/minimal/non-intrusive to me (Olaf, I'm
sure you'll say if you see any problems).

Administratively, I don't see a need to put the minimal comment into
splitup.c -- that's really just recording the original author.  Instead,
please write a ChangeLog entry and commit that along with the changes.
Ok?

Thanks Jonathan.

karl