Add a flag -fno-state-hack, which switches off the "state hack".

It's claims that every function over realWorldStatePrimTy is a
one-shot function.  This is pretty true in practice, and makes a big
difference.  For example, consider
	a `thenST` \ r -> ...E...
The early full laziness pass, if it doesn't know that r is one-shot
will pull out E (let's say it doesn't mention r) to give
	let lvl = E in a `thenST` \ r -> ...lvl...
When `thenST` gets inlined, we end up with
	let lvl = E in \s -> case a s of (r, s') -> ...lvl...
and we don't re-inline E.