Normalize Array.getClass()

It's kind of weird to have the magic Array class implement getClass() directly, which is normally final on Object.  Since we had to special-case it in the compiler anyway, it seems better to just move the implementation there.

http://gwt-code-reviews.appspot.com/658802/show
Review by: tobyr


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@8314 8db76d5a-ed1c-0410-87a9-c151d255dfc7