* `nix-install-package --help' (NIX-9).
* `nix-install-package --non-interactive': don't prompt or pause.
* Tests for nix-install-package.
* Security fixes: filter the values obtained from the nixpkg.
* Removed some dead code (successor stuff) from nix-push.
* Updated terminology in the tests (store expr -> drv path).
* Check that the deriver is set properly in the tests.