[sfepy] Sfepy in Nixpkgs

Just to let you know, Sfepy is now in Nixpkgs.

https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/python-modules...

Unfortunately, the build seems to be broken on master. One test fails in "tests/test_splinebox.py" with

Traceback (most recent call last):
  File "/nix/store/hzh4nqhzr0a86mh1dd8r806cq5sn95pn-python3.7-numpy-1.18.1/lib/python3.7/site-packages/numpy/core/function_base.py",
line 117, in linspace
    num = operator.index(num)
TypeError: 'float' object cannot be interpreted as an integer

If that test is excluded from the build then it builds. I'm assuming that this is an incompatibility between Numpy 1.18.1 and Sfepy 2019.4, which is the current Nixpkgs version of Numpy.

I'm going to repair this by simply omitting that particular test module for now.

-- Daniel Wheeler