With these changes it's possible to override pkgs & lib by:
```
emacs.pkgs.override { pkgs = fooPkgs; }
```
and get them to coherently apply to all emacs packages.
With these changes it's possible to override pkgs & lib by:
```
emacs.pkgs.override { pkgs = fooPkgs; }
```
and get them to coherently apply to all emacs packages.