Fix AutoBean VM memory leak due to circular references between the
ProxyAutoBean, ShimHandler, and WeakReference.
Issue 6193.
http://gwt-code-reviews.appspot.com/1448803
Patch by: bobv
Review by: tbroyer, rjrjr


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10201 8db76d5a-ed1c-0410-87a9-c151d255dfc7