nsqlookupd: register/unregister cleanup

* add /debug endpoint for tests
* add UNREGISTER test
* actually remove topic registrations
* cleanup channel registrations (but warn) when unregistering a topic
* improve AddProducer/RemoveProducer so we can log more clearly when
  things are happening (and also improve general logging)
nsqd: move responsibility of notifying to topic/channel Delete()
test: expand cluster tests

* add a bit of sleep in between testing daemons that just started
Merge pull request #134 from mreiferson/registration_fixes_134

nsqd/nsqlookupd: registration fixes
nsqd: remove support for identification in SUB; remove old process metadata format
nsqd: make MPUB an atomic operation
Merge pull request #135 from mreiferson/atomic_mpub_135

nsqd: atomic MPUB
Merge pull request #132 from mreiferson/deprecate_132

nsqd: clean up deprecated code