FreeBSD/NetBSD makefs sync

[Ed Maste <emaste%freebsd.org@localhost>]

I and some other FreeBSD developers are interested in syncing our copy
of makefs with changes that have happened in NetBSD, to pick up msdos
support and other changes. I started a thread on the FreeBSD-arch list
[1] to discuss different approaches of updating our makefs, and
passing on to NetBSD changes that are only in our tree.

I've discovered a few differences with options, and would like to
mention them here in the hope that we can avoid introducing new
incompatible use of option letters.

FreeBSD's has an option that is currently not taken in NetBSD's makefs:
-D    Treat duplicate paths in an mtree manifest as warnings not error.

We originally used -p as the sparse option but have now deprecated it
in favour of -Z.

We recently introduced an incompatible -r option (to round up the
image size). I've noted that in FreeBSD PR 203707 [2] which provided
the patch, and it's been updated to use -R instead.

We don't yet have -O (offset) in FreeBSD.

[1] https://lists.freebsd.org/pipermail/freebsd-arch/2015-October/017376.html
[2] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=203707