Commit 5643714 introduced a tiny
bug, neglecting to pass the `pkgs` parameter to `release.nix`.

This bug went unnoticed because commit
e663518 had introduced a much larger
bug: an attribute collision resulted in `stdenvBootstrapTools` being
shadowed, and therefore never evaluated.  As a result, the missing
`pkgs` parameter did not lead to an error.

This commit passes the missing parameter so that fixing the
larger/earlier bug will not cause an eval failure.

`stdenvBootstrapTools` was defined in both `nixpkgs` and `releases`
jobsets. This makes hydra view a bit confusing:

    $ git grep -F 'stdenvBootstrapTools =' | cat
    pkgs/top-level/all-packages.nix:  stdenvBootstrapTools = if stdenv.hostPlatform.isDarwin then
    pkgs/top-level/release.nix:      stdenvBootstrapTools = with lib;

The change renames jobset to be distinct. At least it improves grep
experience.

…local jobs

This change exposes symbol override that accidentally caused job loss on hydra:

    $ nix repl ./release.nix
    error: jobs: Unexpected attribute collision between 'jobs' and 'pkgs': stdenvBootstrapTools

Added assert makes sure attribute clashes would not be re-introduced.

This brings two benefits:

1. The complete list of collisions is printed in the whenever any colliding
   attribute is accessed.

2. The sets are intersected using a C++ primitive, which runs in O(n) time
   (intersecting pre-sorted lists) with small constants rather than interpreted
   Nix code.

Thanks to @toonn for prompting this improvement.