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/TreeViewer.java
return ((TreeItem) o).getItems();
		}
		if (o instanceof Tree) {
			return ((Tree) o).getItems();
		}
		return null;
	}
	/*
	 * (non-Javadoc) Method declared in Viewer.
	 */
	public Control getControl() {
		return tree;
	}
	/*
	 * (non-Javadoc) Method declared in AbstractTreeViewer.
	 */
	protected boolean getExpanded(Item item) {
		return ((TreeItem) item).getExpanded();
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.viewers.ColumnViewer#getItemAt(org.eclipse.swt.graphics.Point)
	 */
	protected Item getItemAt(Point p) {
		return getTree().getItem(p);
	}
	/*
	 * (non-Javadoc) Method declared in AbstractTreeViewer.
	 */