- 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

zfsboottest: sync with changes in zfs boot code

- spa status can not be called before spa init
- libzfs.h inclusion is now required
- fix alternative code for explicit root dataset lookup

MFC after: 10 days

zfsboottest: update for the recent zfs boot code changes

MFC after: 1 month

- Allow to specify multiple files to check, eg.

zfsboottest gpt/system0 gpt/system1 - /boot/kernel/kernel /boot/zfsloader

- Instead of printing file's content calculate MD5 hash of the file,
so it can be easly compared to the hash calculated via file system.
- Some other minor improvements.

MFC after: 3 days

zfsboottest: some additional enhancements

- redirect diagnostics printfs in the boot code to stderr
- do not read trailing garbage from a trailing block of a file

Also add my copyright to the file after making so many changes.

Approved by: re (kib)
MFC after: 1 week

zfstest: rename to zfsboottest and move to tools

Approved by: re (kib)
MFC after: 1 week

zfstest: cleanup the code, improve functionality and diagnostics

The utility is not connected to the build, so it should be safe
to update it.
To do: move the utility to tools/.
Some code is provided by Peter Jeremy <peterjeremy@acm.org>

Tested by: Sebastian Chmielewski <chmielsster@gmail.com>,
Peter Jeremy <peterjeremy@acm.org> (earlier versions)
Approved by: re (kib)
MFC after: 4 days

A simple test harness to help debug problems with the ZFS boot code.