This class allows the merge algorithm to be customized to work for the
various merge types. The supported merge types are:
- Spy map merge - This merge inserts active proxy recognition information
into an ObjectMap.
- Local to Shared map merge - This merge adds the newer nodes in a local
map to the shared map it was derived from.
- Local->Local or Shared->Shared map merge - These merges are required by
the CM merge algorithm to handle processing in multiple views.