[Catalog-sig] PEP 345 Update

["Martin v. Löwis"]

> 1/ The obsolete field could be used to say "this is the new version of
> X", like "the name of the project has changed". So the new version
> obsoletes the old one. Using this field, I think that the installers
> should remove the old releases (by prompting the user).

In case of "obsoletes", it _should_ also be possible to install both
of them simultaneously. Maybe some other other distribution depends
on the original one, and can't work with the new one.

Regards,
Martin