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

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Adds sha256 support. While it is a good idea to also add sha384 and
sha512, I did not do that since it is not entirely clear where "the one
true place" to hold their implementations is going to be. Sha256 is
different since mtree already links against libmd.

Make recommended procedure for integrity checking in the manpage
consistent.

Fix a bug with -f spec1 -f spec2 comparison, which prevented
test/tes03.sh from running successfully.

Reviewed by: phk, cperciva

Remove extra "*/".

Per letter dated July 22, 1999 remove 3rd clause of Berkeley derived software
(with permission of addtional copyright holders where appropriate)

Improve spec to spec comparison output.

The new "spec against spec" comparison code was yet another time
victim of the special sort order employed where files come before
directories and alphabetic inside these two groups.

Approved by: re@

Give mtree(8) the ability to take [two -f spec] arguments and compare
the two specifications to each other.