Refactor and simplify the main task scheduling and poll loops:

Refactor and simplify the main task scheduling and poll loops:

* Make output handlers unregister themselves and call wait() to notify
  exit listeners immediately. This makes the exit listeners more useful
  for scheduling tasks. This makes the poll loop nice an clean because
  it just calls the handlers and then the handlers can do the scheduling
  when necessary.

* Make SequentialTaskQueue.add() and addFront() trigger scheduling
  internally, so that it's more of a chain reaction than something that has
  to be done explicitly.

svn path=/main/trunk/; revision=11013