The core type-matcher Unify.match was previouly using tcView to expand
types, because it must treat newtypes as distinct from their representation.
But that meant that it also treated the PredType {C Int} as distinct from
its representation type (:TC Int).  And that in turn was causing a rule
not to fire, because the argument types didn't match up.

For this to happen we need to get a situation where we have

  a = :DC blah blah	-- Dictionary
  ....(f a).....

Now a has type (:TC Int), bu the RULE for f expects an argument 
of type {C Int}.  Roman found that just this was happening.