define a non-public hook for receiving all events from the event handler
define a non-public hook for receiving all events from the event handler

If we're going to be dispatching events via a threadpool that's possibly running
user code, we don't want to be in contention with that code for receiving important
state notifications from the event thread. This method gets *all* events, so be smart.

zk-ruby/zk,rickypai/zk