- Reset stable/10 back to -PRERELEASE status now that releng/10.4
has been branched.
- Update __FreeBSD_version to reflect the new -STABLE branch.
- Switch the pkg(8) configuration for the default installation and the
DVD image creation back to the latest set, i. e. revert r322737.

Approved by: re (implicit)

Switch the pkg(8) configuration for the default installation and the
dvd1.iso to use the quarterly set, i. e. 2017Q3, during the 10.4-BETA
phase.

Approved by: re (implicit)

MFC r263937:

Give hint on how to disable the default repository.

MFC r258227 (bapt):
Enabled should be a boolean, not a string

Approved by: re (glebius)
Sponsored by: The FreeBSD Foundation

MFC r257668:

Use proper capitalization for FreeBSD.org

Approved by: bapt
Approved by: re (gjb)

MFC r257667:

Enable fingerprint checking as the currently known
fingerprint has an uploaded signature on all mirrors.

Approved by: bapt
Approved by: re (gjb)

MFC r257344,r257403:

Move /etc/keys to /usr/share/keys where users are less likely to modify them.

Approved by: bapt
Approved by: re (gjb)

MFC: r256770,r257142,r257145,r257146,r257147,r257148,
r257149,r257150,r257158,r257159,r257164,r257168,
r257193

- Support checking signature for pkg bootstrap from remote
and for 'pkg add ./pkg.txz'

- Be verbose on where pkg is being bootstrapped from.

- Add support for reading configuration files from /etc/pkg.
For now only /etc/pkg/FreeBSD.conf is supported.

- Add test package signing key fingerprint into /etc/keys/pkg/trusted.

- Disable fingerprint checking by default for now as the official
packages are not yet signed.

Approved by: bapt
Approved by: re (glebius)

Add support for reading configuration files from /etc/pkg.
For now only /etc/pkg/FreeBSD.conf is supported. Its style is:

Repo: {
URL: "...",
MIRROR_TYPE: "...",
...
}

The configuration will be read from /usr/local/etc/pkg.conf if exists,
otherwise /etc/pkg/FreeBSD.conf

Approved by: bapt
MFC after: 2 days