This seems to have combined badly with the systemd upgrade, we'll revert for now and revisit after the 14.04 branch. This reverts commit ad80532881, reversing changes made to 1c5d3c7883.
ad80532881
1c5d3c7883
Nixpkgs is a collection of packages for Nix package manager. Nixpkgs also includes NixOS linux distribution source code.