Regression introduced by 2e34288f0d.
The commit in question just used the "lib" attribute, but it wasn't in
scope. In addition to bringeng the lib attribute into scope, I also
removed the "with lib;", which should make sure that we get an error
when just parsing (nix-instantiate --parse) the Nix expression.
Signed-off-by: aszlig <aszlig@nix.build>
2f30e32121