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
}
		return null;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.viewers.StructuredViewer#doUpdateItem(org.eclipse.swt.widgets.Widget,
	 *      java.lang.Object, boolean)
	 */
	protected void doUpdateItem(Widget widget, Object element, boolean fullMap) {
		if (widget instanceof Item) {
			final Item item = (Item) widget;
			
			if (fullMap) {
				associate(element, item);
			} else {
				Object data = item.getData();
				if (data != null) {
					unmapElement(data, item);
				}
				item.setData(element);
				mapElement(element, item);
			}
			int columnCount = doGetColumnCount();
			if (columnCount == 0)
				columnCount = 1;
			
			
			for (int column = 0; column < columnCount || column == 0; column++) {
				ViewerColumn columnViewer = getViewerColumn(column);