Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

MFC r266553, r266554:

r266553:
Add forward-compatibility glue with pkg-1.3:
- Use ASSUME_ALWAYS_YES=YES instead of ASSUME_ALWAYS_YES=1
since pkg-1.3 expects "yes" or "true" values.
- Before exporting PKG_ABI, strip extra characters from what
is parsed from 'pkg -vv'. This causes problems further down
when creating the packages directory for inclusion on the
dvd1.iso. Previously PKG_ABI would be 'freebsd:9:x86:64',
but now is '"freebsd:9:x86:64";' in pkg-1.3.

r266554:
Disable the main FreeBSD pkg(7) repositories in the dvd
repository configuration to avoid fetching from upstream
in case there may be conflicts.

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

MFC r258305, r258770, r259400, r259426:

r258305:
Use the IMAGES variable to determine which image files to
remove as part of 'make -C /usr/src/release clean'.

r258770 (hrs):
Add NOPKG to disable pkg-stage.

r259400:
Reduce disc1.iso size by 74MB by removing lib32 libraries,
sendmail, and atf.

r259426:
Add a pkg(8) repository configuration file for cdrom-based
package installation.

As part of the 'pkg-stage' target, copy the configuration
file to the 'packages/repos/' directory on the DVD filesystem.

Sponsored by: The FreeBSD Foundation

Add a pkg(8) repository configuration file for cdrom-based package
installation.

As part of the 'pkg-stage' target, copy the configuration file
to the 'packages/repos/' directory on the DVD filesystem.

MFC after: 3 days
X-MFC-Before: -RC3
Sponsored by: The FreeBSD Foundation