Adds support for Class.getSuperclass() needed to implement Enum.getDeclaringClass().  The corresponding test cases were updated accordingly.

Patch by: mmendez
Review by: scottb (postmortem, tweaked in r1605)

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@1590 8db76d5a-ed1c-0410-87a9-c151d255dfc7