Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Introduce the PRECIOUSPROG knob in bsd.prog.mk, similar
to PRECIOUSLIB from bsd.lib.mk. The side effect of this
is making installing the world under jail(8) possible by
using another knob, NOFSCHG.

Reviewed by: oliver

Only check if ENABLE_SUID_NEWGRP is defined, for consistency with
other ENABLE_SUID_* variables.

Add the newgrp(1) utility, which changes groups. This is required by
the POSIX.2 UPE.

PR: 36190
Reviewed by: -standards, silence on -audit