Change setup.py not to import poppy before it's installed
AstroPy tests if NumPy is installed during setup, even though we don't need it then (astropy/package-template#107)
Warn of weird NumPy setuptools interactions in setup
Make explicit the dependency on scipy and matplotlib
Update astropy_helpers to v0.4.2
Merge pull request #11 from josePhoenix/master

Improve robustness of setup.py in the absence of certain dependencies