This provides a more reliable way to determine that we are definitely imported from an astropy source checkout, by checking for a file .astropy-root that would only ever possibly exist in this case.  This is inessential though and can be removed if people want to get rid of this extra top-level file.
Actually this is better; we can put the special .astropy-root file under static/ so that it's not cluttering up the actual root.  But this is good enough for the desired purposes.
Add an explanation to .astropy-root
If extension modules need to be recompiled, automatically try running build_ext --inplace rather than just failing to import--very convenient.  At some point this should be extended to work for any extension module (rather than just using the utils._compiler heuristic) but that could be a little trickier
Fixed support on Python 3, and got rid of .astropy-root per https://github.com/astropy/astropy-helpers/issues/107#issuecomment-64282919
clean wcs tests
Spead up test_all_world2pix significantly with using only the image centre
adding back test
Move relevant np_utils fucns to operations.py to support no ndarray
Make hstack work without structured arrays
Make vstack work without structured arrays
Remove get_groups() from operations
Make join work without structured arrays
Update CHANGES.rst
Deprecate public functions in np_utils
Add message for deprecated np_utils functions [skip ci]
Merge pull request #3179 from taldcroft/table-ops

Remove use of numpy structured arrays in table operations
Merge pull request #3085 from embray/misc/auto-inplace

Auto-build extension modules when importing astropy from source checkout
Make sure to update apt-get listings
Rewrite Unit.__rmul__ and __rdiv__ to speed up array [*/] unit