MFC r215570:

MFC r215570:
  Add to gpart(8) an ability to backup partition table and
  restore it from given backup.

MFC r215671:
  Always dump partition labels with `gpart backup`, but `gpart restore`
  does restore them only when -l option is specified [1]. Make number of
  entries field in backup format optional. Document -l and -r options of
  `gpart show` action.

MFC r215672:
  Add SIGINT handler to `gpart restore` action.

git-svn-id: svn://svn.freebsd.org/base/stable/8@215941 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f