Reenabled multitree dragdrop.

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@9334 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
Improved checkbox selection support for multi dragdrop tree

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@9335 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c