*Possible* fix for #2318.  Not sure if this will fix @cdeil's specific issue, but it *did* fix the issue for me running on my laptop on the institute network.
Check for and prevent initialization of NDData with Quantity

Closes #2374, though admittedly in an unsatisfactory way.
Add changelog entry
correct numerous errors in documentation
Fix docstrings in modeling. Add a note in wcs docstrings about origin of outputs coordinates
Make coeff keyword arguments so that a polynomial with default parameters zeroes can be initialized.
fix typo
Speedup of initialization for cosmology objects

* Speed up initialization by about a factor of 100 by pre-computing
  some unit conversion quantities.  It turns out this was the
  dominant cost, particularly the call to const.G.cgs.
* import astropy.cosmology time falls by about 50%
* Passes all unit tests
* Closes #2479 (sorta; some more sophisticated options were
  also discussed for that, and this just does the simple bit).
PEP8ify cosmology.core
Allow NDData and uncertainty to be set with Quantity
Fixes for @nhmc comments, more pep8ification.
Tweak to remove unnecessary ' in coordinates index
Added missing "the"
Include astropy-helpers in the tarball.
rewording according to discussion on github
Remove bdist_dmg functionality since .dmg disk images are no longer a commonly used installation mechanism.
Added CHANGES.rst entry
Re-wrote frame documentation
Tweaks to consistent-ify the sgr-example with some recent changes
Update changelog, move entry to New Features