Currently, the deltification of FS nodes occurs during our "stabilization walk"
of the tree during the commit process. The result is that we hold locks longer
than we need to (and more of them), and the deltification is tied to a "commit"
rather than (potentially) becoming an asynchronous operation.
The commit should be completed, then we should walk the revision root (again) to
find the nodes to deltify. Each deltification can then be processed with
(this is somewhere between a defect and an enhancement)
Note: this is a precondition to moving to new Node IDs.