[lltx] input normalization

[Arthur Reutenauer]

> context seems to do input normalization too. Would it be possible to
> add the code to lualatex too?

  I suppose it's not too hard to extract ConTeXt's code, and I also
wrote a standalone implementation five years ago (available from
http://code.google.com/p/google-summer-of-code-2008-tex/downloads/list);
however the problem is that you depend on decomposition data that tends
to be bulky.  ConTeXt keeps all that data (and much more) in
char-def.lua; it's easy enough to extract the relevant parts to do
normalisation, but it's not very satisfactory to duplicate information.

	Arthur