Switch the pkg(8) repository to use the release package set
to populate dvd1.iso.

This is a direct commit to releng/10.2.

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

Update the pkg.conf(5) for the dvd1.iso packages to use the
'quarterly' branch, which was missed in r285830.

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

- Copy stable/10@285827 to releng/10.2 in preparation for 10.2-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.2.
- Update default pkg(8) configuration to use the quarterly branch.[1]

Discussed with: re, portmgr [1]
Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r260772:
Update the pkg-stage target to be more compatible with pkg-1.2:

- Add a release-dvd.conf pkg(8) configuration file to override
the default FreeBSD.conf configuration.
- Remove architecture-specific pkg-stage.conf files, consolidate,
and move their contents to scripts/pkg-stage.sh.
- Use 'pkg -vv' to determine the ABI, which is used as the
cache directory.

Prior to these changes, it would be possible for pkg-stage to fetch
conflicting binary packages from multiple repositories.

Tested against: head@r260522, stable/10@r260522

Sponsored by: The FreeBSD Foundation

Update the pkg-stage target to be more compatible with pkg-1.2:

- Add a release-dvd.conf pkg(8) configuration file to override
the default FreeBSD.conf configuration.
- Remove architecture-specific pkg-stage.conf files, consolidate,
and move their contents to scripts/pkg-stage.sh.
- Use 'pkg -vv' to determine the ABI, which is used as the
cache directory.

Prior to these changes, it would be possible for pkg-stage to fetch
conflicting binary packages from multiple repositories.

Tested against: head@r260522, stable/10@r260522

MFC after: 3 days
X-Insta-MFC: possibly
Sponsored by: The FreeBSD Foundation