Also some cosmetic improvements.

This reduces the size of the closure by 45 MiB.

Ubuntu 17.10 doesn't have libbrotli.

https://hydra.nixos.org/build/79867741

Dead code since https://github.com/NixOS/nixpkgs/commit/6669a3b47711dc967df0ea8ff93fa9857aad015d

It's all dead code since 2014 (commit 0c6d62cf).

Fedora 27 provides an incompatible version of Boost (1.64.0).

https://hydra.nixos.org/build/73991153

This failed because NixOS' release.nix calls builtins.fetchGit.

 - darwin installer: delete hardware report, not necessary
 - moves os-specific code from the darwin installer to to `poly_*`
   functions
 - adds profile.d support to the profile targets, which automatically
   handles many distros which don't have a /etc/bashrc but do have an
   /etc/profile.d
 - /bin/bash -> /usr/bin/env bash
 - document why each excluded shellcheck check is excluded
 - rename the multi-user to Daemon-based

pathsFromGraph is legacy since Nix 2.0.

The release does not in fact depend on Ubuntu/Fedora builds (we don't
publish the build results).

Note that this only requires headers from boost so it doesn't add a
runtime dependency.

Also, use Nixpkgs 18.03.

Probably should point at the 18.03 release branch once that's made.

This makes it easier to provide a default, e.g.

  system = builtins.currentSystem or "x86_64-linux";

In this mode, the following restrictions apply:

* The builtins currentTime, currentSystem and storePath throw an
  error.

* $NIX_PATH and -I are ignored.

* fetchGit and fetchMercurial require a revision hash.

* fetchurl and fetchTarball require a sha256 attribute.

* No file system access is allowed outside of the paths returned by
  fetch{Git,Mercurial,url,Tarball}. Thus 'nix build -f ./foo.nix' is
  not allowed.

Thus, the evaluation result is completely reproducible from the
command line arguments. E.g.

  nix build --pure-eval '(
    let
      nix = fetchGit { url = https://github.com/NixOS/nixpkgs.git; rev = "9c927de4b179a6dd210dd88d34bda8af4b575680"; };
      nixpkgs = fetchGit { url = https://github.com/NixOS/nixpkgs.git; ref = "release-17.09"; rev = "66b4de79e3841530e6d9c6baf98702aa1f7124e4"; };
    in (import (nix + "/release.nix") { inherit nix nixpkgs; }).build.x86_64-linux
  )'

The goal is to enable completely reproducible and traceable
evaluation. For example, a NixOS configuration could be fully
described by a single Git commit hash. 'nixos-rebuild' would do
something like

  nix build --pure-eval '(
    (import (fetchGit { url = file:///my-nixos-config; rev = "..."; })).system
  ')

where the Git repository /my-nixos-config would use further fetchGit
calls or Git externals to fetch Nixpkgs and whatever other
dependencies it has. Either way, the commit hash would uniquely
identify the NixOS configuration and allow it to reproduced.

The VM was running out of RAM while handling debug symbols, which caused the
eu-strip to fail while separating debug symbols.

In particular, using fetchGit means we don't need hackery to clean the
source tree when building from an unclean tree.

E.g.

  $ nix eval '(fetchMercurial https://www.mercurial-scm.org/repo/hello)'
  { branch = "default"; outPath = "/nix/store/alvb9y1kfz42bjishqmyy3pphnrh1pfa-source"; rev = "82e55d328c8ca4ee16520036c0aaace03a5beb65"; revCount = 1; shortRev = "82e55d328c8c"; }

  $ nix eval '(fetchMercurial { url = https://www.mercurial-scm.org/repo/hello; rev = "0a04b987be5ae354b710cefeba0e2d9de7ad41a9"; })'
  { branch = "default"; outPath = "/nix/store/alvb9y1kfz42bjishqmyy3pphnrh1pfa-source"; rev = "0a04b987be5ae354b710cefeba0e2d9de7ad41a9"; revCount = 0; shortRev = "0a04b987be5a"; }

  $ nix eval '(fetchMercurial /tmp/unclean-hg-tree)'
  { branch = "default"; outPath = "/nix/store/cm750cdw1x8wfpm3jq7mz09r30l9r024-source"; rev = "0000000000000000000000000000000000000000"; revCount = 0; shortRev = "000000000000"; }

This fixed the build on ubuntu/debian, where dash is the sh.