Supported locales list update

[Bruno Haible]

> At least those UTF-8 locales that are most likely to be used in FAQs and
> HOWTOs as examples should also appear in the localedata/SUPPORTED list.

Also, and more importantly, all @euro locales should have an UTF-8
locale listed in localedata/SUPPORTED. This will allow people in these
European countries to change their encoding once only instead of twice
(ISO-8859-1 -> ISO-8859-15 -> UTF-8).

Bruno