- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

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

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

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

Add a small testcase for the new -f-f mode.