hammer2 - Add destroy-inum directive

hammer2 - Add destroy-inum directive

* Add support for destroying screwed up inodes (e.g. inodes with CRC
  failures and such).

  hammer2 -s filesystem destroy-inum inode_number

  This will attempt to destroy an inode number without reading it,
  allowing the removal of dead inodes from a corrupted filesystem.

* This is similar to 'hammer2 destroy path', which destroys dead
  directory entries, but acts on the inode instead of on the
  directory entry.