Fix setup.py to match it's current paster template

[mikkonieminen]

Fixes plugin's setup.py namespace_packages to match the updated setup.py paster template. Fixes the issue mentioned in e.g. here: ckan/ckan#2893

[torfsen]

@mikkonieminen Note that the problem in ckan/ckan#2893 was that extensions did not declare ckanext as a namespace package. That some extensions additionally declare their ckanext.<name> package to be a namespace package is usually not required but shouldn't cause any problems.

(That also applies to your other PRs, ckan/ckanext-report#13, ckan/ckanext-qa#41, ckan/ckanext-archiver#32)

[mikkonieminen]

@torfsen We are having a strange issue when installing the extensions with pip and Ansible but, when the ckanext.<name> namespace package is removed the issue goes away. Installation with python setup.py develop however works either way.

[torfsen]

@mikkonieminen That's interesting. I've encountered a similar issue: you cannot mix editable and non-editable installations for sub-packages of the same namespace-package using pip. See pypa/pip#3 for details. As a result we're installing all our CKAN extensions in editable mode (pip install -e ...).

Since ckanext.<name> usually isn't required to be a namespace package (in contrast to ckanext) I see no problem in removing it (as your PR does) if that fixes your problems.

[amercader]

Yes, this caused some obscure problems in the past, thanks @mikkonieminen