ReactiveX/RxJava — pull request #1802 by simonbasle (2014-10-27 11:17:28+00:00)
Title: add hasObservers method to Subjects (#1772)

as per https://github.com/ReactiveX/RxJava/issues/1772

SerializedSubject now keeps track of the actual Subject.
BufferUntilSubscriber synchronizes on the state guard.