First attempt at using MiniConda for affiliated packages

Just to test if it's going to work nicely like the core package, or whether it will require more work (because of the astropy installation)
Conda includes astropy by default, so I don't think this is necessary.

if you do want to explicitly have astropy installed then it should be done in the install step with ``numpy=`` to avoid upgrading numpy when you install astropy -- if you do ``conda install -c astropy-ci-extras --yes astropy`` then conda looks for the most recent astropy (0.3.2), checks its numpy version (1.8) and upgrades both numpy and astropy.

Looks like conda itself provides astropy 0.3.2 in python 2.[67] and 3.[34] only for numpy=1.8 (you can see what they build with ``conda search astropy``