Patient.setIdentifiers accepts args it shouldn't

Patient.setIdentifiers will allow you to specify a new set of identifiers, and takes whatever set you give it. However, later on, it is necessary to cast that set to a SortedSet, and not all Sets can be cast. (In particular, Collections.singletonSet cannot.) Patient.setIdentifiers should copy the argument set instead.

Easy to work around, but should be fixed because it is hard to debug when it happens, since the error appears to come from deep within Hibernate.