Fixes a bug in JavaScriptObject support in DevMode that prevents dispatching
through an interface to a method defined in a super-interface. The change
also includes a new test to serve as a regression test.

Review at http://gwt-code-reviews.appspot.com/1287801
Review by: bobv, scottb, cromwellian


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9542 8db76d5a-ed1c-0410-87a9-c151d255dfc7