- gcdIntzh_fast, cmpIntegerIntzh_fast, cmpIntegerzh_fast,
  integer2Intzh_fast, and integer2Wordzh_fast all used the
  unboxed tuple return convention, which isn't quite right
  since they're just returning unboxed values. Fixed.

- similarly for forkzh_fast, it was using an unboxed value
  return convention, ought to be doing an unboxed tuple
  return.


Both of these broke the unregisterised build -- it still not
sane, more debugging to be done.