…' availability

The previous method with getsitepackages was a bit fragile
because it is not always clear to which directory the package
is installed
(it can be pythonX/site-packages or pythonX.Y/dist-packages
or a variation on these).

… installed package

…in an installed package

The package is not always installed (for example, when a user prefers
to work with the source code directory, without `pip install -e .`.

…thon and SciPy