detect already available python dependencies

[evils]

libsmu v1.0.3 used to detect python dependencies that were already provided
with a9e8546, the installation no longer does this (except for setuptools)

in my nix package i relied on that to build the python bindings
it's probably possible to make the current build/install process work with nixpkgs,
but it is beyond my nix python tooling know-how

(the problem with v1.0.4 being that it tries to fetch the python dependencies from the internet, which isn't allowed in the isolated nix build environment)