This change makes overrides to the janeStreet set work as expected by
making the janeStreet set take part in the ocamlPackages fixpoint for
janeStreet 0.14, i. e. OCaml >= 4.08

This change makes overrides to the janeStreet set work as expected by
making the janeStreet set take part in the ocamlPackages fixpoint for
janeStreet 0.12, i. e. OCaml == 4.07

This change makes overrides to the janeStreet set work as expected by
making the janeStreet set take part in the ocamlPackages fixpoint for
janeStreet 0.11, i. e. OCaml < 4.07

Previously, we inherited non-janestreet ocaml dependencies from super
and janestreet dependencies from self which always was super.janeStreet.

This behavior is however not really what we want due to liftJaneStreet:
Users and other packages will use ocamlPackages.base etc. instead of
ocamlPackages.janeStreet.base and the like. Consequently they also would
override the top-level attributes which would mean that other janestreet
packages would not pick up on it however.

As a consequence however, overriding ocamlPackages.janeStreet.base
doesn't work. Since this was never possible, I don't think this is an
issue. It is probably a good idea to deprecate that set anyways and
printing a warning when it is used via trace.

janeStreet_0_9_0 is unchanged as the disticniton between self and super
makes sense for it.

Below is an example showing how overriding would work from an user's
perspective:

test-overlay.nix:

    self: super: {
      ocamlPackages = super.ocamlPackages.overrideScope (old: _: {
        base = old.base.overrideAttrs (_: {
          meta.broken = true;
        });
      });
    }

nix-repl> (import ./. { overlays = [ (import ./test-overlay.nix) ]; }).ocamlPackages.
stdio
error: Package ‘ocaml4.10.0-base-0.14.0’ in /home/lukas/src/nix/nixpkgs/pkgs/development/ocaml-modules/janestreet/janePackage_0_14.nix:12 is marked as broken, refusing to evaluate.

a) To temporarily allow broken packages, you can use an environment variable
   for a single invocation of the nix tools.

     $ export NIXPKGS_ALLOW_BROKEN=1

b) For `nixos-rebuild` you can set
  { nixpkgs.config.allowBroken = true; }
in configuration.nix to override this.

c) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
  { allowBroken = true; }
to ~/.config/nixpkgs/config.nix.