---------------------------------------
	Fix a long-standing CSE bug with unboxed tuples
	  ---------------------------------------

		Merge to stable

Consider
        case f x of
	  (# a,b #) -> if a>0
		       then f x -- CSE opportunity
		       else (# b,a #)

 GHC 6.2's CSE pass wrongly optimised this to:

	case f x of t
	  (# a,b #) -> if a>0 then
			  t	-- WRONG
			else (# b,a #)

(Wrong because we aren't allowed to mention a case binder for
an unboxed-tuple case.)

This commit fixes the problem.