This doesn't work in read-only mode, ensuring that operations like

  nix path-info --store https://cache.nixos.org -S nixpkgs.hello

(asking for the closure size of nixpkgs.hello in cache.nixos.org) work
when nixpkgs.hello doesn't exist in the local store.

Now you get

  [
    {
      "path": "/nix/store/fzvliz4j5xzvnd0w5zgw2l0ksqh578yk-bla",
      "valid": false
    }
  ]

On second though this was annoying. E.g. "nix log nixpkgs.hello" would
build/download Hello first, even though the log can be fetched
directly from the binary cache.

May need to revisit this.

Multi-user installer for Darwin (master edition)

Also output in the status report that the user is very silly

Starve the TTY of input to ensure this works, but provide yes to the
current installer to handle the current broken case.

Don't install a second nix after the initial installation, and the rsync change fixes a bug hidden by the nix replacement where the store files were being owned by the installing user due to rsync's -a implying -og.

relevant directions

Prompt for sudo before validating assumptions, and check ourselves for root-owned files instead of making a scary warning.

Fixes #1464.

Not really necessary anymore for #849, but still nice to have.

Fixes #849.

Fix potential crash/wrong result two hashes of unequal length are compared

Clearer error message when regex exceeds space limit

Not sure about the raw ellipsis.