Exposes the built-in year-month-weekday-day format in PredefinedFormat.

Review at http://gwt-code-reviews.appspot.com/1039801

Patch by: guillaume.ryder
Review by: jat


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9129 8db76d5a-ed1c-0410-87a9-c151d255dfc7