TST: sdist and then install with `pip` on travis
TST: sdist and then install with `pip` on travis

to test that all necessary files have been included in `MANIFEST.in`,
which does *not* happen when installing from source with:

`pip install .`

tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control