This makes memoization of Nixpkgs evaluation less effective, since
some Nixpkgs invocations may have 'config = {}' while others may have
'config = { xorg = {}; }'.
Instead set 'config = {}'.
*** NixOS *** NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at http://nixos.org/nixos and in the manual in doc/manual.