[XeTeX] XeLaTeX and SIunitx

[Joseph Wright]

Hello all,

Taking a look back over the code, I already have some auto-detection in
for picking up UTF-8 symbols when the correct engine is in use.

I've revised this a bit for the next release (v2.5d, on CTAN tomorrow),
so that all of the 'problematic' symbols are covered in what seems to be
the best way possible. Nothing happens unless appropriate support
(fontspec/unicode-math) is loaded. If it is, then you get the following
symbols:

 - Ångström       u+00c5 (u+212b normalises here)
 - Degree Celsius u+00b0 + "C" (u+2103 is a compatibility character)
 - Micro          u+00b5 (u+03bc is wrong)
 - Ohm            u+03a9 (u+2126 normalises here)

 - Degree     u+00b0
 - Arc minute u+2032 (requires unicode-math)
 - Arc second u+2033 (requires unicode-math)
-- 
Joseph Wright