1.0.16.16: Use declared element type in AREF short-circuit transform

1.0.16.16: Use declared element type in AREF short-circuit transform
	The short-circuit transformation introduced in 1.0.2.17
	removed the system's understanding of the declared array element
	type (as opposed to the upgraded array element type).
	Reintroduce the cleverness, and hope that the use of type=
	doesn't remove all the slowdown.

	(Issue noted by vy on #lisp afternoon 2008-05-04 BST)