anchor.diff:  FROM registry.services.nersc.gov/nersc/intel_cxx_fort_mpi_mkl_devel as builder
   
  -RUN apt -y update && apt install -y apt-utils && echo yes
  +RUN apt -y update && apt install -y apt-utils && echo 3
   
   RUN DEBIAN_FRONTEND=noninteractive \
       apt install -y --no-install-recommends \
  
positive.code:   && python -c "from astropy.coordinates import EarthLocation, SkyCoord, AltAz; from astropy.time import Time; print(EarthLocation.of_site('ctio')); print(SkyCoord(180.,-45.,unit='deg').transform_to(AltAz(obstime=Time(56806.0, format='mjd'), location=EarthLocation.of_site('ctio'))))"
  
  # Patch astropy:
  ADD urlmap-readonly.patch /tmp/
  RUN cd /usr/local/lib/python3.5/dist-packages && \
      patch -p1 < /tmp/urlmap-readonly.patch
  
  # Alternatively, could retrieve
  #   http://data.astropy.org/coordinates/sites.json
  
negative.code:     && make clean \
      && (cd && PYTHONPATH=/usr/local/lib/python python3 -c "import astrometry; print(astrometry.__version__)")
  
  RUN pip --no-cache-dir install cython
  
  # The Tractor
  RUN git clone http://github.com/dstndstn/tractor.git tractor \
  