* The simplifier used to glom together all the top-level bindings into
  a single Rec every time it was invoked.  The reason for this is explained
  in SimplCore.lhs, but for at least one simple program it meant that the
  simplifier never got around to unravelling the recursive group into
  non-recursive pieces.  So I've put the glomming under explicit flag
  control with a -fglom-binds simplifier pass.   A side benefit is
  that because it happens less often, the (expensive) SCC algorithm
  runs less often.