Added remove_audio() and remove_chat() skeleton methods to Session

darcs-hash:20090224183000-58103-d92231d166422f3ca8d68eb8ddd02988ca31131e
fix NotifyFromThreadObserver to respect 'condition' argument

darcs-hash:20090225100548-b2873-f61328a7803f6d9b69403305fdd5b9b3b8b26933