... in the ruby shebang test.

nix-daemon: Exit successfully when interrupted.

Fixes #2058.

fix typo in nix-env man page

Fix missing $DESTDIR when installing programs and BUILD_SHARED_LIBS=0

The test fakes the interpreter only to verify the arguments it would be
given.

The ported code in 80ebc553 was incorrectly ported.

```
-            $envCommand = "exec $execArgs $interpreter -e 'load(\"$script\")' -- ${\(join ' ', (map shellEscape, @savedArgs))}";
...
+                    envCommand = (format("exec %1% %2% -e 'load(\"%3%\") -- %4%") % execArgs % interpreter % script % joined.str()).str();
```

The single-quote finishing the small ruby snippet was lost in
translation.

Make the TTL for disk cache configurable

rename the options to mention it's a narinfo TTL as disk cache is used all over the place for other operations

re-order the options using the alphabetical order and improve the example in the positive lookup case

disk cache lookup for example by doing:
  nix copy --from <binary-cahe> <store-path> --option \
  positive-disk-cache-ttl 0

Issues: #1885 #2035

document that writeTextFile from Nixpkgs is an alternative to toFile

Fixes

  error: getting status of '/nix/store/j8p0vv89k1pf0cn7kmfsdcs7bshwga1i-firefox-52.7.2esr/share/icons/hicolor/48x48/apps/firefox.png': No such file or directory

https://github.com/NixOS/nix/issues/1934

Also improve error message on directory/non-directory collisions.

Fixes https://github.com/NixOS/nix/issues/1934 (at least the "error:
opening directory '/nix/store/...-linux-config-4.4.14': Not a
directory" issue).

Expand the multi-user installer to support Linuxes with systemd

We use grep instead of an equality check because it is difficult
to extract _just_ the user's note, instead it is prefixed with
some plist junk. This was causing the user note to always be set,
even if there was no reason for it.

Grep would ignore files that didn't exist, but would complain
about files in a directory if the directory didn't exist. Simply check
for the directory first, prior to grepping it.

nix copy: add an example with S3

I couldn't find a good example how to use it with non-us-east-1 buckets.

 - 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

Fixes https://github.com/NixOS/nix/issues/2009.

Document fetchGit.

release.nix: Use pkgs.closureInfo for binaryTarball

pathsFromGraph is legacy since Nix 2.0.

Fixes #1981.