MFC:

MFC:
r241684,245316,245318,245440,245563,245565,245622,245754,246092,246096,246602

r241684:
Allow LOCAL_DIRS to install files in directories not found in the
system mtree files via a LOCAL_MTREE variable which contains a list of
mtree files to be applyed along with the base mtree files to the tmp
root and DESTDIR.

r245440:
Add an option DB_FROM_SRC to use src/etc's user/group databases when
installing.  This allows things like running installworld for 10-CURRENT
on a 9.0-RELEASE system without adding extra users and groups to the
passwd and group files.

To prevent potentially risky uid/gid mismatches on systems with
non-standard local values, require that DESTDIR be set if DB_FROM_SRC is
set.

Sponsored by:   DARPA, AFRL
Reviewed by:    peter

r245565:
Rework the mtree portion of etc/Makefile's distrib-dirs target to run
mtree in a shell loop so there is only one mtree commandline.  Move the
implementation of LOCAL_MTREE into etc/Makefile.

Sponsored by:   DARPA, AFRL

git-svn-id: svn://svn.freebsd.org/base/stable/9@248335 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f