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
* @see #getCurrentLocation()
     */
    public static final int LOCATION_AFTER = 2;
    /**
     * Constant describing the position of the cursor relative 
     * to the target object.  This means the mouse is positioned
     * directly on the target.
     * @see #getCurrentLocation()
     */
    public static final int LOCATION_ON = 3;
    /**
     * Constant describing the position of the cursor relative 
     * to the target object.  This means the mouse is not positioned
     * over or near any valid target.
     * @see #getCurrentLocation()
     */
    public static final int LOCATION_NONE = 4;
    /**
     * The viewer to which this drop support has been added.
     */
    private Viewer viewer;
    /**
     * The current operation.
     */
    private int currentOperation = DND.DROP_NONE;
    /**
     * The last valid operation.  We need to remember the last good operation
     * in the case where the current operation temporarily is not valid (drag over
     * someplace you can't drop).  
     */