MFC r245311:

Add pwcache(3) and vis(3) to libegacy as install(1) is about to grow a
dependency on them.

Sponsored by:	DARPA, AFRL
MFC all changes to install(1) through r246784.  Notable functional
changes are:

r245617:
Introduce six new options from NetBSD:
 * -M <metalog>   Log metadata in mtree format.
 * -D <destdir>   Log paths relative to <destdir>.
 * -h <hash>      Log digest of type <hash>.
 * -T <tags>      Specify which mtree tags to log.
 * -l <linkflag>  Create hard or symbolic links (allows logging).
 * -U             Install without root privileges (owner, group, mode,
                  and flags can be logged via -M

NOTE: In the interest of compatibility with NetBSD and because it is the
obvious letter, the nearly useless -M option (disable mmap) has been
repurposed.

Sponsored by:	DARPA, AFRL
Obtained from:	NetBSD
Reviewed by:	bz

r245312:
Implement the -N <dbdir> option which allows an alternate passwd and
group file to be used.  This is useful for installing on systems where
a user or group does not currently exist.

Sponsored by:	DARPA, AFRL
Obtained from:	NetBSD
MFC r245751,245893:

r245751:
Implement the -l option using ln(1) to facilitate boostrapping.

Ignore the new options -D, -h, -T, and -U.  Adjust -M support to ignore
an argument.

Sponsored by:	DARPA, AFRL
Reviewed by:	ian, ray, rpaulo

r245893:
Use = not == in test arguments.

Submitted by:	Christoph Mallon <christoph.mallon@gmx.de>