Substitute "types.uniq types.string" -> "types.str"
Manual: Fix -I flag
Export only the files of the active definitions
Add some option types
Show correct position info for errors in submodules

E.g.

  The unique option `fileSystems./.device' is defined multiple times, in `/etc/nixos/configuration.nix' and `/etc/nixos/foo.nix'.

This requires passing file/value tuples to the merge functions.
smartd.nix: Fix broken option type