Bug 232777 [Viewers] ViewerDropAdapter holds currentTarget forever
Build ID: 3.3.2 Member currentTarget should be set to null after drop or after cancel, because it holds a domain object, which can't be garbage collected after Viewer.setInput(null).
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerDropAdapter.java
* @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);
	/**
	 * Overrides the current operation for a drop that happens immediately
	 * after the current validateDrop.
	 * 
	 * This maybe called only from within a
	 * {@link #validateDrop(Object, int, TransferData)} method
	 * 
	 * 
	 * @param operation
	 *            the operation to be used for the drop.