HAMMER 26/many: Misc features.

HAMMER 26/many: Misc features.

* Add an inode flag to lock the transaction id used to update the inode
  on-disk.  This is used for both inode creation and rename to synchronize
  the inode with the related directory entry so historical lookups do not
  get confused.

* Add a capability to prune all deleted records.

* Properly set the file size for softlinks to reflect the length of
  the softlink string (fixes a NFS issue).

* Add additional device checks to the mount code to detect block devices
  which are already in use.

* Implement the noatime mount option.

* Implement a poor-man's fakename for NFS when backing out of a historical
  access.

* Properly connect ".." for a renamed directory to the new parent directory.