MFC r221788:

MFC r221788:
  Add basic metadata integrity check. In case when partition table was
  probed and read successfull, but it contains invalid values (e.g.
  overlapped partitions, offset or size is out of bounds), then table
  will be rejected.

MFC r221972:
  Add a sysctl kern.geom.part.check_integrity for those who has corrupt
  partition tables and lost an ability to boot after r221788.
  Also unhide an error message from bootverbose, this would help to
  easier determine the problem.

MFC r221984:
  Add diagnostic messages for integrity checks.

MFC r221992:
  Make diagnostic messages more specific. With bootverbose print out
  all inconsistencies of integrity in the partition table, not first
  found only.

MFC r222642:
  Add diagnostic message about not aligned partitions.

git-svn-id: svn://svn.freebsd.org/base/stable/8@230567 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f