hammer2 - small-embedded-data fixes, syncer fixes

hammer2 - small-embedded-data fixes, syncer fixes

* Add a bit of a hack to try to fix an issue where the embedded data
  would sometimes not get synchronized.  Add the DIRTYEMBED flag
  and test for it in various places.

* Remove an improper call to hammer2_chain_modify() on the inode
  (the previous handling of embedded data, which was broken).

* Detect and dispose of unlinked files from vop_inactive.

* Fix some inefficiencies in the flush code.  When modifying a chain
  in order to update its blockref array hammer2_chain_modify() was
  recursively setting SUBMODIFIED upward, messing up the flush code's
  sequencing and causing it to not completely flush the topology.

* Remove some debugging.