HAMMER 56F/Many: Stabilization pass
* When data is reblocked any related direct-io offsets cached in front-end
buffer cache buffers must be cleaned out. This also requires running
through any snapshotted inodes referencing the same object.
* The flusher must check that the cached B-Tree node has not been flagged
as deleted (HAMMER_NODE_DELETED) before seeking to it.
* hammer_io_direct_read() now requires and asserts that the second-level
cached offset in the BIO is a zone-2 offset.
* hammer_io_direct_write() no longer overwrites the second-level cached
offset with the third level raw disk offset. It pushes a third level
to set the raw disk offset.
* When creating a directory entry, set the localization field for pseudo-fs
support (which isn't quite working yet anyway so no biggy).
* Move the Red-Black tree generator for inodes from hammer_ondisk.c to
hammer_inode.c.