HAMMER 26/many: More NFS support work, rename fixes
* Add a fakename return argument to vop_nlookupdotdot(). This allows HAMMER
to supply a fake name for historical (@@<timestamp>) transitions when
regenerating the namecache topology. The feature is needed when operating
as a NFS server.
* Do not mark a vnode VROOT if it is a historical root rather than the
realtime root. This fixes confusion the namecache has when dealing
with the root vnode of a HAMMER filesystem.
* Fix a bug in nrename(). ino_data.parent_obj_id was not being properly
adjusted when moving directories.