-------------------------------
		Fix a fundep bug
	-------------------------------

		MERGE TO STABLE

Big thank-you to Martin Sulzmann for finding this functional dependency bug.

The new defn of FunDeps.Equation is:
	type Equation = (TyVarSet, [(Type, Type)])
Before it was (TyVarSet, Type, Type), so each pair of types was separately
quantified (wrong).

It's important that we have a *list* of pairs of types.  Consider
 	class C a b c | a -> b c where ...
	instance C Int x x where ...
Then, given the constraint (C Int Bool v) we should improve v to Bool,
via the equation ({x}, [(Bool,x), (v,x)])
This would not happen if the class had looked like
	class C a b c | a -> b, a -> c


Test in typecheck/should_compile/tc180