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	   Mainly PredTypes (28 Sept 00)
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Three things in this commit:

	1.  Main thing: tidy up PredTypes
	2.  Move all Keys into PrelNames
	3.  Check for unboxed tuples in function args

1. Tidy up PredTypes
~~~~~~~~~~~~~~~~~~~~
The main thing in this commit is to modify the representation of Types
so that they are a (much) better for the qualified-type world.  This
should simplify Jeff's life as he proceeds with implicit parameters
and functional dependencies.  In particular, PredType, introduced by
Jeff, is now blessed and dignified with a place in TypeRep.lhs:

	data PredType  = Class  Class [Type]
		       | IParam Name  Type

Consider these examples:
	f :: (Eq a) => a -> Int
	g :: (?x :: Int -> Int) => a -> Int
	h :: (r\l) => {r} => {l::Int | r}

Here the "Eq a" and "?x :: Int -> Int" and "r\l" are all called
*predicates*, and are represented by a PredType.  (We don't support
TREX records yet, but the setup is designed to expand to allow them.)

In addition, Type gains an extra constructor:

	data Type = .... | PredTy PredType

so that PredType is injected directly into Type.  So the type
	p => t
is represented by
	PredType p `FunTy` t

I have deleted the hackish IPNote stuff; predicates are dealt with entirely
through PredTys, not through NoteTy at all.


2.  Move Keys into PrelNames
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This is just a housekeeping operation. I've moved all the pre-assigned Uniques
(aka Keys) from Unique.lhs into PrelNames.lhs.  I've also moved knowKeyRdrNames
from PrelInfo down into PrelNames.  This localises in PrelNames lots of stuff
about predefined names.  Previously one had to alter three files to add one,
now only one.

3.  Unboxed tuples
~~~~~~~~~~~~~~~~~~
Add a static check for unboxed tuple arguments.  E.g.
	data T = T (# Int, Int #)
is illegal