Add Collection<Set<ServiceName>> ServiceContainer.detectCircularity() method.

This method should scan the container and find, on a best-effort basis, all service cycles, returning them as a collection of sets of service names where each set is a distinct cycle (in other words, do not return the same cycle in a permuted order). All service names should be the primary names. The sets should be unmodifiable and should have a consistent equals() and hashCode(), so that consumers can cache sets to avoid reporting the same problem multiple times.