hammer2 - major simplification 1/many (stabilization)

hammer2 - major simplification 1/many (stabilization)

* Fix a dirty chain leak due to detached inodes and the delayed vnode
  deactivation that DragonFly does.  A cache_unlink() call was missing
  to properly cycle the vnode in the nrename path and a
  hammer2_cluster_delete() needed the DELETE_PERMANENT flag to handle the
  case where the vnode was already detached.

* Fix an inode reference count leak, callers of hammer2_inode_common_parent()
  were not properly dropping the returned inode.

* Fix a deadlock due to front-end vs write-thread interactions.  nvtruncbuf()
  calls must not be made with an inode lock held.

* Cleanup some debugging, add some debugging.