bug#52834: sanity-check fails with namespace packages

[Lars-Dominik Braun]

Hi Hartmut,

> These fail due to sanity-check not being able to import "zope" - which 
> is a namespace package. Both use the "src directory layout" (source is 
> contained in a sub-directory "src").
As far as I see PEP 420 (implicit namespace packages) is supported by
Python >=3.3 only, so I’m not sure the packages would work even if we
disabled 'sanity-check, do they? Either way, I’m in favor of removing
broken Python 2 packages.

> This could be solved by fetching a list og namespace-packages and 
> checking whether a fails import is a namespace-package. Maybe there are 
> other solution.
> […]
>       nspkgs = set(dist.get_metadata_lines('namespace_packages.txt'))
Depending on undocumented setuptools behavior should imo be avoided and
– for top_level.txt – phased out if possible.

Cheers,
Lars