Problem with osx-64

[megies]

Trying to run the tests on the install done from the built installer runs into an error (e.g. https://travis-ci.org/obspy/anaconda-installers/jobs/253951757#L672):

$ $HOME/obspy-anaconda/bin/python -m obspy.scripts.runtests --no-flake8 -n anaconda-installers -r
/Users/travis/obspy-anaconda/bin/python: 
Importing the multiarray numpy extension module failed.  Most
likely you are trying to import a failed build of numpy.
If you're working with a numpy git repo, try `git clean -xdf` (removes all
files not under version control).  Otherwise reinstall numpy.
Original error was: dlopen(/Users/travis/obspy-anaconda/lib/python2.7/site-packages/numpy/core/multiarray.so, 2): Library not loaded: @rpath/libgfortran.3.dylib
  Referenced from: /Users/travis/obspy-anaconda/lib/libopenblasp-r0.2.19.dylib
  Reason: image not found

It looks a bit like we might suffer from the same problem as described in conda-forge/numpy-feedstock#47 (comment), i.e. a non-working package mix from defaults and conda-forge channels during package selection by constructor.