Fix enum switch construction in GwtAstBuilder.

The existing code breaks on switch(Integer), it tries to tack an ordinal() call on the end of the unbox.

http://gwt-code-reviews.appspot.com/1450815/

Review by: zundel@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10328 8db76d5a-ed1c-0410-87a9-c151d255dfc7