does anyone know if the heated side mirrors come on automatically, or is there a button (rear windshield defrost?) that you must press? i've been driving in unseasonably crappy baltimore weather ever since i got the 2011 limited, and i've had the need for heated mirrors on more than a couple occasions. that said, do the mirrors just come on automatically when there's a drop in temperature? i'm still trying to figure this one out -- the owner's manual doesn't mention anything about the heated mirrors.