Setting the default selection model in DefaultNodeInfo to null. Having a selection model per node is almost always incorrect. Users should supply a single Selectionmodel for the entire tree in most cases.

Review at http://gwt-code-reviews.appspot.com/657801

Review by: rice@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@8326 8db76d5a-ed1c-0410-87a9-c151d255dfc7