This reverts commit 5e3ad1dd. Manual
generation now depends on the 'nix' command.

This means we don't have two (divergent) sets of option descriptions
anymore.

The default CSS puts almost no space between sections, but a lot of
space between subsections. This flips that around.

Don't try to parse signature check as commit timestamp

Co-authored-by: Eelco Dolstra <edolstra@gmail.com>

Offer a safer interface for path and pathOpt

Make `system-features` a store setting

Add hashed-mirrors back

Make narHash in ValidPathInfo not optional

When the log.showSignature git setting is enabled, the output of
"git log" contains signature verification information in addition to the
timestamp GitInputScheme::fetch wants:

  $ git log -1 --format=%ct
  gpg: Signature made Sat 07 Sep 2019 02:02:03 PM PDT
  gpg:                using RSA key 0123456789ABCDEF0123456789ABCDEF01234567
  gpg:                issuer "user@example.com"
  gpg: Good signature from "User <user@example.com>" [ultimate] 1567890123
  1567890123

For folks that had log.showSignature set, this caused all nix operations
on flakes to fail:

  $ nix build
  error: stoull

Include a long comment explaining the policy. Perhaps this can be moved
to the manual at some point in the future.

Also bump the daemon protocol minor version, so clients can tell whether
`wopBuildDerivation` supports trustless CA derivation building. I hope
to take advantage of this in a follow-up PR to support trustless remote
building with the minimal sending of derivation closures.

Use `TeeSink` and `TeeSouce` in a few more places

Separate auth and logic for the daemon

Fix `wopNarFromPath` which needed a `toRealPath`.

This seems more correct. It also means one can specify the features a
store should support with --store and remote-store=..., which is useful.
I use this to clean up the build remotes test.

Before, processConnection wanted to know a user name and user id, and
`nix-daemon --stdio`, when it isn't proxying to an underlying daemon,
would just assume "root" and 0. But `nix-daemon --stdio` (no proxying)
shouldn't make guesses about who holds the other end of its standard
streams.

Now processConnection takes an "auth hook", so `nix-daemon` can provide
the appropriate policy and daemon.cc doesn't need to know or care what
it is.

demote remote build message to Info

Two small derivation serialization cleanups

Always reset ANSI colors in progress-bar line

When having a message like `waiting for a machine to build X` and
building with `nix build -L`, the log-prefix is always colored yellow[1]
on a small terminal-width as everything (including the ANSI color-reset) is
stripped away.

To work around that problem, this patch explicitly adds an `ANSI_NORMAL`
to the end of the line.

[1] https://imgur.com/a/FjtJOk3

The name is now stored with the derivation itself.

These are not supposed to include the 'name' part of the store
path. This was broken by 759947bf.

Fixes #3872.

This is a bit hacky. Ideally we would automatically re-evaluate the
failed attribute iff we need to print the error message (so in
commands like 'nix search' we wouldn't re-evaluate because we're
suppressing errors).