Bug 12585 Packages view should not provide file and resource transfer if Java element below CU is selected
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/dnd/DelegatingDragAdapter.java
private TransferDragSourceListener[] fPossibleListeners;
	private List fActiveListeners;
	private TransferDragSourceListener fFinishListener;
	
	public DelegatingDragAdapter(TransferDragSourceListener[] listeners) {
		Assert.isNotNull(listeners);
		fPossibleListeners= listeners;
	}
	
	/* non Java-doc
	 * @see DragSourceListener
	 */
	public void dragStart(DragSourceEvent event) {