TODO

   1
   2 - check superblock checksum in examine DONE
   3 - report "chunk" or "rounding" depending on raid level DONE
   4 - report "linear" instead of "-1" for raid level DONE
   5 - decode ayout depending on raid level DONE
   6 - get Assemble to upgrade devices if force flag.
   7 - --verbose and --force flags.
   8
   9 - set md_minor, *_disks for Create  - DONE
  10 - for create raid5, how to choose between
  11    all working, but not insync
  12    one missing, one spare, insync
  13 - when RUN_ARRAY, make sure *_disks counts are right
  14
  15 - get --detail to extract extra stuff from superblock,
  16    like uuid  DONE
  17 - --detail --brief to give a config file line
  18 - parse config file. DONE
  19 - test...
  20
  21 - when --assemble --scan, if an underlying device is an md device,
  22   then try to assemble that device first.
  23
  24
  25 - mdctl -S /dev/md0 /dev/md1 gives internal error