patch applied (hugs98): get MonadFix(mfix) from Hugs.Prelude instead of Control.Monad.Fix

[Ross Paterson]

Tue Jun 19 17:05:26 PDT 2007  Ross Paterson <ross at soi.city.ac.uk>
  * get MonadFix(mfix) from Hugs.Prelude instead of Control.Monad.Fix
  
  Thus we can use mdo even if mfix is not in scope.

    M ./docs/users_guide/hugs_ghc.xml -2 +3
    M ./libraries/hugsbase/Hugs/Prelude.hs +5
    M ./src/static.c -62 +1
    M ./src/type.c -19 +9