Add a HasKey interface and a maxColumns param for SideBySideTreeView Note: the location of the getKey() method needs further thought Review at http://gwt-code-reviews.appspot.com/277801 Review by: jgw@google.com git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@7805 8db76d5a-ed1c-0410-87a9-c151d255dfc7