Add a hasParent() DAG method for Sync of deleted objects.

Let the DAG track the deleted object versions.  Sync uses
hasParent() to handle cases of parent-to-child mutations
where either parent or child may be a deleted version:
- parent-to-delete: object deletion
- delete-to-child: conflict resolution revives the object
- parent-to-child: object update

Change-Id: Ibe7c67cba60190e706f2769410ab466f8d43c4d6
30 files changed
tree: 13cd52d5ee90ba2a736331c64b2095a3b86da7ef
  1. examples/
  2. lib/
  3. products/
  4. runtimes/
  5. security/
  6. services/
  7. tools/