This was preventing the Nixpkgs channel from updating, since the
program indexer barfed on:
error: anonymous function at /nix/store/wdnwbh3kmf68nhqqp0khcyxbdbp43vg5-nixos-14.12.626.b0d594c/nixos/nixpkgs/pkgs/top-level/node-packages.nix:1:1 called without required argument ‘neededNatives’, at /data/releases/nixos/unstable-small/.tmp-nixos-16.03pre72946.c50d013-787/unpack/nixos-16.03pre72946.c50d013/lib/customisation.nix:56:12
because Nixpkgs 16.03 was importing files from Nixpkgs 14.12.
Also added some half-assed checks to detect this issue in the future.
* package statsd node packages separatly since they actually require
nodejs-0.10 or nodejs-0.12 to work (which is ... well old)
* remove statsd packages and its backends from "global" node-packages.json.
i did not rebuild it since for some reason npm2nix command fails. next time
somebody will rerun npm2nix statsd packages are going to be removed.
* statsd service: backends are now provided as strings and not anymore as
packages.
