This is important because this contains some code copied from nix (as an
interim expediency until that functionality can be exported via nix's
API). The license specified here must be compatible with this borrowing.
Select the same license that nix is released under: lgpl2Plus.
Also add --all, which shows the value of all options. Diffing the --all
output on either side of contemplated changes is a lovely way to better
understand what's going on inside nixos.
