[XeTeX] Don't update to Mac OS X 10.6.7

[Mojca Miklavec]

To those Mac users who updated too early,

>From what I read, Apple has confirmed the bug and is working on the
patch (still nobody knows when it will be released).

In the meantime the user KJK555 from a forum suggested to replace
ATS.framework and submited an unofficial patch:
   https://discussions.apple.com/thread/2792142?start=300&tstart=0
   http://azlist.info/kj/downloads/

I didn't test extensively (you need to apply it at your own risk), but
some of my documents that were causing me problems now print fine***.

Mojca

*** stars explained on the context list; I should not complain about
macs too much on this list :)