Workaround for illegal package merging in py-matplotlib/py-basemap (#1964)

* Workaround for illegal package merging in py-matplotlib/py-basemap

# Conflicts:
#	var/spack/repos/builtin/packages/py-basemap/package.py

* flake8

* flake8

* Be conservative: only apply the namespace package fix for Python >= 3.5.2

* flake8

* Bug fix