Bug 167323 [Viewers]Open AbstractTreeViewer for external widget implementors
As reported by Ross Camara AbstractTreeViewer would work for nebula if we would open the API a bit. Boris and I decided that we will do this in 2 steps: 1. open the API 2. moving the Virtual-Support bits from TreeViewer to AbstractTreeViewer when the nebula grid provides virtual support.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTableViewer.java
* @param element
	 *            the element to add
	 */
	public void add(Object element) {
		add(new Object[] { element });
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.viewers.StructuredViewer#doFindInputItem(java.lang.Object)
	 */
	protected Widget doFindInputItem(Object element) {
		if (equals(element, getRoot())) {
			return getControl();
		}
		return null;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.viewers.StructuredViewer#doFindItem(java.lang.Object)
	 */
	protected Widget doFindItem(Object element) {
		Item[] children = doGetItems();
		for (int i = 0; i < children.length; i++) {
			Item item = children[i];
			Object data = item.getData();
			if (data != null && equals(data, element)) {
				return item;
			}