Also fix some setup hooks that unnecessarily used environment hooks, which revolted in the same variable being modified too many times.
Adds a couple of useful NetBSD and OpenBSD derivations. Some of these will be integrated into Nixpkgs later. Noncomprehensive list: - netbsd.getent - netbsd.getconf - netbsd.fts - openbsd.mg - netbsd.compat (can replace libbsd)