Windows builds failing due to weird crash

Depending on how far down the rabbit hole this goes I might just make a temporary workaround for this on Windows.

Right now the builds are failing on Windows due to the automatic generation of the default astropy.cfg file, which is run in a subprocess.  The call the `Popen.communicate()` is crashing, and from trial and error it seems to have something to do with passing environment variables. More as I investigate this...