New build system for es.utf, pt.utf8, pt_BR.utf8

> I've committed new build system for pt.utf8, es.utf8 and pt_BR.utf8. 
> The most important change is that it is no longer needed to
> maintain two copies of maxima.texi in /<lang> and /<lang>.utf8.
> Make imports all required data from /<lang> and recodes it to utf8. 
> maximahtml.mk files no longer in use either.

Thanks a lot; this makes things easier.

-- 
Mario Rodriguez Riotorto
www.biomates.net