The SSHStore PR adds this functionality to the daemon, but we have to
handle the case where the Nix daemon is 1.11.

Also, don't require signatures for trusted users. This restores 1.11
behaviour.

Fixes https://github.com/NixOS/hydra/issues/398.

For example, you can now set

  build-sandbox-paths = /dev/nvidiactl?

to specify that /dev/nvidiactl should only be mounted in the sandbox
if it exists in the host filesystem. This is useful e.g. for EC2
images that should support both CUDA and non-CUDA instances.

Fixes #1084

Fix SIGFPE from integer overflow during division

On some architectures (like x86_64 or i686, but not ARM for example)
overflow during integer division causes a crash due to SIGFPE.
Reproduces on a 64-bit system with:

    nix-instantiate --eval -E '(-9223372036854775807 - 1) / -1'

The only way this can happen is when the smallest possible integer is
divided by -1, so just special-case that.

The removal of CachedFailure caused the value of TimedOut to change,
which broke timed-out handling in Hydra (so timed-out builds would
show up as "aborted" and would be retried, e.g. at
http://hydra.nixos.org/build/42537427).

The store parameter "write-nar-listing=1" will cause BinaryCacheStore
to write a file ‘<store-hash>.ls.xz’ for each ‘<store-hash>.narinfo’
added to the binary cache. This file contains an XZ-compressed JSON
file describing the contents of the NAR, excluding the contents of
regular files.

E.g.

  {
    "version": 1,
    "root": {
      "type": "directory",
      "entries": {
        "lib": {
          "type": "directory",
          "entries": {
            "Mcrt1.o": {
              "type": "regular",
              "size": 1288
            },
            "Scrt1.o": {
              "type": "regular",
              "size": 3920
            },
          }
        }
      }
      ...
    }
  }

(The actual file has no indentation.)

This is intended to speed up the NixOS channels programs index
generator [1], since fetching gazillions of large NARs from
cache.nixos.org is currently a bottleneck for updating the regular
(non-small) channel.

[1] https://github.com/NixOS/nixos-channel-scripts/blob/master/generate-programs-index.cc

Done slightly differently from https://github.com/NixOS/nix/pull/1093.

This caused the gc test to fail on Darwin.

.gitignore: catch up with perl -> c conversion

This was broken since ff0c0b64. Since
I can't figure out how to mount a devpts instance in the sandbox,
let's just bind-mount the host devpts.

http://hydra.nixos.org/build/42025230

Commit 86e8c67e broke it, because
CURL_* are not actually #defines.

This prevents collisions with the "native" OpenSSL, in particular on
OS X.

Fixes #921.

This allows the binary cache substituter to pipeline requests.

override rx directory permissions in deletePath()