Bug#212921: cdebconf: Merge in new translations in templates

[Petter Reinholdtsen <pere@hungry.com>]

[Denis Barbier]
> I do not understand, debconf-loadtemplate already allows this, what
> else do you need?

As far as I know, it will _replace_ the existing translations, not
just add new ones.

That means that if you have template 'foo' with translations 'foo-es',
and then load a new template file with template 'foo' and translation
'foo-nb', the 'foo-es' translation is dropped.  I want the database at
that point to contain both 'foo', 'foo-es' and 'foo-nb'.