HAMMER 40A/Many: Inode/link-count sequencer.
* Remove the hammer_depend structure and build the dependancies directly
into the hammer_record structure.
* Attempt to implement layout rules to ensure connectivity is maintained.
This means, for example, that before HAMMER can flush a newly created
file it will make sure the file has namespace connectivity to the
directory it was created it, recursively to the root.
NOTE: 40A destabilizes the filesystem a bit, it's going to take a few
passes to get everything working properly. There are numerous issues
with this commit.