Handle Validation of Cascaded Generic properties.
Make GwtValidators Singletons.

[JSR 303 TCK Result] 88 of 257 (34.24%) Pass with 38 Failures and 14 Errors.

Review at http://gwt-code-reviews.appspot.com/1343801

Review by: rchandia@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9678 8db76d5a-ed1c-0410-87a9-c151d255dfc7