----------------------------------------
	Class ops that do not introduce for-alls
	----------------------------------------

	MERGE TO STABLE (if poss)

The handling of class ops that do not add an extra for-all
was utterly bogus.  For example:

	class C a where
	    fc :: (?p :: String) => a;

	class D a where
	    fd :: (Ord a) => [a] -> [a]

De-bogus-ing means

a) Being careful when taking apart the class op type in
	MkIface.tcClassOpSig

b) Ditto when making the method Id in an instance binding.
   Hence new function Inst.tcInstClassOp, and its calls
   in TcInstDcls, and TcClassDcls