MFC r258305, r258307, r258308, r258309, r258310, r258314, r258317,
r258319, r258320:

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

r258307:
  Add a script and configuration files to fetch pre-built packages
  from pkg.FreeBSD.org for inclusion on release medium (dvd1.iso).

r258308:
  Unconditionally copy the build host /etc/resolv.conf into
  the chroot directory, since hostname resolution may be
  needed in the case of building a dvd image (with packages)
  and also setting 'NOPORTS=1'.

r258309:
  Set the PKG_CACHEDIR directory to 'dvd/' instead of 'release/'
  in preparation of adding a 'dvd1.iso' target.

r258310:
  Add the 'dvd1.iso' target.  This mimics the 'release.iso' target,
  with the additional step of fetching packages for inclusion on the
  dvd image.

  The 'pkg-stage' target is used to run 'scripts/pkg-stage.sh' if
  the '${TARGET}/pkg-stage.conf' configuration file exists (currently
  only amd64 and i386).

  Allow dvd1.iso to be skipped if NODVD=1.

r258314:
  Fix how ABI is evaluated so it matches more than a dot-zero
  case.

r258317:
  Document the 'dvdrom' target.

r258319:
  Remove WITHOUT_PROFILE=1 for the dvd1.iso medium.

r258320:
  Simplify PKG_ABI for pkg-stage.sh.

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