It seems to be no longer possible to call -retain from -dealloc with the latest libobjc2, which was causing the tests to fail.
We are also throwing an exception in this case, which would need to be specifically caught in order for the resurrection to be of value to users, so this simply removes the -retain call and resets the singleton variables to nil in order to not have invalid pointers and for the singletons to be re-created on subsequent access.
