Pretty print unboxed tuples with spaces

The output of the pretty printer for `MagicHashUnboxedTuple.hs` was 

    {-# LANGUAGE MagicHash, UnboxedTuples #-}
    module MagicHashUnboxedTuples where
    
    f (#x, y#) = (#a#,  b#) where
      a# = a#
      b = b

But this was not parseable because `b#` is a single token.