See https://bitbucket.org/pypa/setuptools/issue/130/install_data-doesnt-respect-prefix

This is currently needed for some packages like xpra.

• update Python docs
• fix packages using the current workaround
• open PR upstream

Current workaround for xpra: https://github.com/NixOS/nixpkgs/blob/master/pkgs/tools/X11/xpra/default.nix#L45