Loads a cache from ids to cubbies based on the root objects and a neighborhood function.
the cubbies to start with.
the neigborhood function from cubbies to (refslot,collection) pairs.
How far from the root are we allowed to travel. If maxDepth == 0 no ids are added to the cache, for maxDepth == 1 only the roots are added to the cache, for maxDeptn == 2 the roots immediate children etc.
an existing cache. Cubbies with ids in this cache will not be loaded/traversed.
a cache that maps ids to the cubbie objects in the graph defined by the roots, neighborhood function and maximum depth.