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     1. Make primOpIsCheap do something sensible
     2. Make the state hack work better
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1.  In March 2001, we changed primOpIsCheap to
	primOpIsCheap op = False
thereby making *no* primops seem cheap.  But this killed eta
expansion on case (x ==# y) of True -> \s -> ...
which is bad.  In particular a loop like
  doLoop n = loop 0
    where
      loop i | i == n    = return ()
             | otherwise = bar i >> loop (i+1)
allocated a closure every time round because it didn't eta expand.

The problem that made us set primOpIsCheap to False was
		let x = a +# b *# c in x +# x
where we don't want to inline x. But primopIsCheap doesn't control
that (it's exprIsDupable that does) so the problem doesn't occur
even if primOpIsCheap sometimes says 'True'.  I think that perhaps
something changed since March 2001.


2.  Consider this
	case x of
	  True  -> \(s:RealWorld) -> e
	  False -> foo
where foo has arity 1.  If we are using the "state hack" we want to
eta expand here.  This commit fixes arityType in the Var case (for foo)
to take account of foo's type.

Also add -fno-state-hack to the static flags, to allow the state hack to
be switched off.