In order to get all the tests passing the Github repository was
downloaded instead of from pypi so that the `conftest.py` is
available.
In addition to updating the version:
- compatible with 2.7, 3+ now
- all tests are running and passing
The `buildPython*` function computes name from `pname` and `version`.
This change removes `name` attribute from all expressions in
`pkgs/development/python-modules`.
While at it, some other minor changes were made as well, such as
replacing `fetchurl` calls with `fetchPypi`.
