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/ColumnViewer.java
}
	}
	/**
	 * Update the cached cell object with the given row and column.
	 * 
	 * @param rowItem
	 * @param column
	 * @return ViewerCell
	 */
	 ViewerCell updateCell(ViewerRow rowItem, int column) {
		cell.update(rowItem, column);
		return cell;
	}
	/**
	 * Returns the {@link Item} at the given widget-relative coordinates, or
     * <code>null</code> if there is no item at the given coordinates.
	 * 
	 * @param point
	 *            the widget-relative coordinates
	 * @return the {@link Item} at the coordinates or <code>null</code> if there
	 *         is no item at the given coordinates
	 */
	protected abstract Item getItemAt(Point point);
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.viewers.StructuredViewer#getItem(int, int)
	 */
	protected Item getItem(int x, int y) {
		return getItemAt(getControl().toControl(x, y));