dependencies that are *not* propagated to the user environment
(as opposed to `propagatedBuildInputs'). For instance, if you
install `iotop', you typically don't want its Python dependencies
polluting the user environment.
* buildPythonPackage: some cleanup (e.g. use function argument
defaults instead of `if attrs ? foo then attrs.foo else []').
svn path=/nixpkgs/branches/modular-python/; revision=26571
