- 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

Switch the default WARNS level for sbin/ to 6.

Submitted by: Ulrich Spörlein

- Move from mount(2) to nmount(2). This should allow to convert MNT_SNAPSHOT
flag from a mount flag to FS-specific flag.
- Simplify usage. Instead of 'mksnap_ffs /mnt/foo /mnt/foo/snap' allow to
give only one argument: 'mksnap_ffs /mnt/foo/snap'. Old usage is also
accepted for now.
- Add an example of how to mount a snapshot.

Add the mksnap_ffs command to the sbin directory. This setuid root
program allows users in the operator group to take filesystem
snapshots. Its first use will be in support of `dump -L'.

Approved by: Technical Review Board <trb@FreeBSD.org>
Sponsored by: DARPA & NAI Labs.