GitLab

Python 2.6 installer has 10.3 suffix.

See:
https://github.com/matthew-brett/multibuild/issues/24#issue-221951587

Aliased PYTHON_VERSION to MB_PYTHON_VERSION.

Changed the test command to use get_python_enviroment instead of
get_macpython_enviroment.

Extended TravisCI matrix to cover PyPy.
The tests can now tell the implementation of PyPy apart from the CPython
version they emulate.