Bug 263845 [CommonNavigator] Drag/drop folder from non-Java Proj to Java Proj does copy instead of move sometimes
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerDropAdapter.java
*
     * @param exception the exception
     * @param event the event
     */
    protected void handleException(Throwable exception, DropTargetEvent event) {
        
        
        
        exception.printStackTrace();
        event.detail = DND.DROP_NONE;
    }
    /**
     * Performs any work associated with the drop.
     * <p>
     * Subclasses must implement this method to provide drop behavior.
     * </p>
     *
     * @param data the drop data
     * @return <code>true</code> if the drop was successful, and 
     *   <code>false</code> otherwise
     */
    public abstract boolean performDrop(Object data);
	/**
	 * Sets the current operation.
	 * 
	 * This maybe called only from within a
	 * {@link #validateDrop(Object, int, TransferData)} method
	 * 
	 * 
	 * @param operation