[Catalog-sig] New classifiers for Plone

["Martin v. Löwis"]

> You should also include:
> 
> Framework :: Plone
> Framework :: Plone :: 3
> Framework :: Plone :: 4
> 
> to make the set complete.

I think I'll go by what the Plone community decides on. If they
don't need these classifiers, they just don't need them. The fewer
the better.

Regards,
Martin