workaround+RF: always cast floats in read_scalar_data to 64bit
workaround+RF: always cast floats in read_scalar_data to 64bit

    otherwise leads to incorrect rendering (at least on Linux Debian)
    and it is done directly in read_scalar_data so it is in effect for
    add_contour_overlay as well as add_overlay
RF:
	both add_contour_overlay and contour_overlay now use the same
    _read_scalar_data thus allowing for numpy arrays enter into both
    functions (as before it was only add_overlay having this basic
    'factory' built-in)

haribharadwaj/PySurfer,nipy/PySurfer,mwaskom/PySurfer,effigies/PySurfer,diego0020/PySurfer,bpinsard/PySurfer,Eric89GXL/PySurfer