update charset aliases

[Petter Reinholdtsen]

[Bruno Haible]
> Hi,
> 
> Here is a patch to update the charset aliases following changes that
> have been made in http://www.iana.org/assignments/character-sets
> since 2001.

Why do anyone need all these aliases?  Why not force everyone to use
the same name for the same charset?

I do see the rationale for LATIN-9 in addition to ISO-8859-15, but I
fail to see why ISO_8859-15 is needed.

(Hm, but I guess it is to late to complain about this now, that IANA
already accepted the aliases into their standard. :( ))