--------------------------
	Cleanup in DataCon
	--------------------------

	DO NOT merge with stable

The dataConRepStrictness call used to reuturn a [Demand],
but that's a bit misleading.  In particular, consider a  strict
constructor

	data Foo = MkFoo ![Int]

Then the wrapper MkFoo is strict, but the worker $wMkFoo is not.

	MkFoo x = case x of { DEFAULT -> $wMkFoo x }

Nevertheless, when we pattern-match on $wMkFoo we will surely
find an evaluated component to the data structure, and that is
what dataConRepStrictness reports, and that's how it is used
in Simplify.

Solution: make dataConRepStrictness return [StrictnessMark]
not [Demand]. A small matter really.