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.