Implement basic repair for broken directory hardlinks.

[dhoepfl]

• Any hardlink inode with a parent other than the metadata directory is changed
  to have the correct parent.
  I have seen these. I can understand how this happens when a normal directory
  is hardlined for the first time. The journal SHOULD prevent this from being a
  problem but obviously this is not the case.

• Directory hardlink inodes named "temp..." get deleted.
  These directories were deleted while open when the volume was removed without
  unmounting. Since these directories have already been deleted, deleting them
  in fsck is the right thing to do. (Documented like that for files in the HFS+
  spec.)

• Directory hardlink inodes with names other than "temp..." or "dir_..." are moved
  to "lost+found".
  It would be better to rename them to "dir_..." in a first pass, there might still
  be valid links to them. These links are deleted by a different repair step and I
  did not see how to remove those other repair steps. Would probably lead to a bigger
  rewrite of the hardlink check code so I decided to just move these to l+f.
  I have never seen this anyways.

[dhoepfl]

Neither the first nor the third error should happen in a journaled filesystem (directory hardlinks require the Journal to be active). My guess is that using HFS+ over AFP (as TimeMachine does) does not correctly persist the journal before persisting changes. Thus loosing the connection during directory hardlink operation can result in partially executed atomic operation.