Follow up to r10350. Allow collapse-all-properties in .gwt.xml module files

Fixes issues: 5694

Review at http://gwt-code-reviews.appspot.com/1463806

Review by: rjrjr@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10470 8db76d5a-ed1c-0410-87a9-c151d255dfc7