[XeTeX] Patches for XeTeX installation scripts (XeTeX on FreeBSD + more)

[Jonathan Kew]

Hi Nikola,

Many thanks for this; it looks like a good step forward in general,  
and I hope we can include these improvements.

One issue I notice is the use of realpath(1) in the scripts. This is  
a problem, as it is not universally available; it's not present on  
Mac OS X, for example. Are there any good alternative approaches?

Jonathan