- changing an object's name after construction is not allowed. Checks are performed
  when adding objects to parents that no duplicate names are used, changing the name
  to a duplicate name after adding it is therefore allowed and voids internal
  consistency.

- check for race in _task_pause()/_stop() since the TASK_LOCK is not held by the
  calling thread and the STREAM_LOCK not by the task code.

- only emit EOS in PLAYING.

- implement state change order on get<->loop-get<->loop elements.