Despite Apple’s claims of much stronger aluminosilicate glass for the iPhone 4, Engadget is reporting that the back of their iPhone 4 review unit is scratched after just five days of use. Omitted in the blog’s full review, the scratches—described as “nasty”—only became visible in bright light. While iFixIt’s teardown indicated that the iPhone 4’s front panel is made of Gorilla Glass, the service company…