-----------------------------
	Put existential tyvars second
	[fixes ParsecPerm lint error]
	-----------------------------

In an existential data constr:

	data Eq a => T a = forall b. Ord b => MkT a [b]

the type of MkT is

	MkT :: forall a b . Ord b => a -> [b] -> MkT a

Note that the existential tyvars (b in this case) come *after*
the "ordinary" tyvars.

I had switched this around earlier in the week, but I'm putting
it back (and fixing a bug) because I found it really works better second.

Reason: in a case expression we may find:
	case (e :: T t) of { MkT b (d:Ord b) (x:t) (xs:[b]) -> ... }
It's convenient to apply the rep-type of MkT to 't', to get
	forall b. Ord b => ...
and use that to check the pattern.  Mind you, this is really only
use in CoreLint.