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
}
	/**
	 * Creates a generic viewer column for the given column widget, based on the given label provider.
	 * 
	 * @param columnOwner the column widget
	 * @param labelProvider the label provider to use for the column
	 * @return ViewerColumn the viewer column
	 */
	private ViewerColumn createViewerColumn(Widget columnOwner,
			CellLabelProvider labelProvider) {
		ViewerColumn column = new ViewerColumn(this,columnOwner) {};
		column.setLabelProvider(labelProvider, false);
		return column;
	}
	/**
	 * Activate the support for custom tooltips.
	 */
	public void activateCustomTooltips() {
		if (tooltipSupport == null) {
			tooltipSupport = new ToolTipSupport(this);
		} else {
			tooltipSupport.activate();
		}
	}
	/**
	 * Deactivate the support for custom tooltips.
	 */
	public void deactivateCustomTooltips() {
		if (tooltipSupport != null) {
			tooltipSupport.deactivate();