----------------------------------
	Implement Typeable properly
	----------------------------------

1.  Add 'deriving' for Typeable class. So you can say

	data T a b = .... deriving( Typeable )

    At the moment you only get this if you ask for it. If you say
    nothing you get nothing.

2.  Implement Typeable better, with proper O(1) comparison of
    type representations

3.  Add the 'cast' operation described in 'Scrap your boilerplate'
    and use it.


4.  Consequence: need to move the definition of IOArray from
    Data.Array.IO.Internals to GHC.IOBase, where it joins IORef.
    This is necssary so that HashTable can be low down in the compilation
    hierarchy, and hence so can Dynamic.



	WARNING: I'm not certain the imports in HashTable and Dynamic
		 will all be right for Hugs and NHC. I hope you can
	  	 fix them up.