[Distutils] namespace package doesn't get its __init__.py file if --single-version-externally-managed

[zooko]

The full version is here:

https://bugs.launchpad.net/zope3/+bug/146373

The short version is that if you run ./setup.py install --single- 
version-externally-managed from the zope.interface 3.4.0 source tree,  
you'll get everything you need to import zope.interface except for  
the "zope/__init__.py" file.

Is this a bug in setuptools?

Regards,

Zooko