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
}
    /**
     * Returns the current {@link DropTargetEvent}.
     * 
     * This may be called only inside of the {@link #validateDrop(Object, int, TransferData)} 
     * or {@link #performDrop(Object)} methods.
     * @return the DropTargetEvent
     * @since 3.5
     */
    protected DropTargetEvent getCurrentEvent() {
    	Assert.isTrue(currentEvent != null);
    	return currentEvent;
    }
    
    /**
     * Returns whether visible insertion feedback should be presented to the user.
     * <p>
     * Typical insertion feedback is the horizontal insertion bars that appear 
     * between adjacent items while dragging.
     * </p>
     *
     * @return <code>true</code> if visual feedback is desired, and <code>false</code> if not
     */
    public boolean getFeedbackEnabled() {
        return feedbackEnabled;
    }
    /**
     * Returns the object currently selected by the viewer.
     *
     * @return the selected object, or <code>null</code> if either no object or