fixed a bug where .xs_super was a class where it should have been a prototype
troubleshot an issue with duplicate destination due to false positive dection of sentinel in fetch due to empty arrays. Also proposal for check against duplicate destinations in _add_destination(), see source
Ugly implementation that works with clients doing .add()s on subscribers but break encapsulation big time and introduce weird emit_emit_xxx methods and even weirder emit_add & code pseudo operations, the model is broken, needs a fix
fix bug where tracer was calling the wrong super constructor