This is not entirely trivial since this introduces the possibility
of mutual recursion.
* Made normal forms self-contained.
* Use unique ids, not content hashes, for content referencing.
archives (using the package in corepkgs/nar).
* queryPathByHash -> expandHash, and it takes an argument specifying
the target path (which may be empty).
* Install the core Fix packages in $prefix/share/fix. TODO: bootstrap
Nix and install Nix as a Fix package.