Eta expansion wibbles
~~~~~~~~~~~~~~~~~~~~~
* Don't eta reduce, and do eta expand,
  data con workers and primops

  Reason: they don't have bindings, so they aren't really
  ordinary variables.

This is a bit of a swamp, provoked by moving CoreSat later,
something I'm beginning to wonder about...

Not are things settled yet -- I think some rules may
not fire that should because of constructor worker/wrapper
issues.  E.g when you have   foldr (:) [] xs = xs