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
}
	/**
	 * The column viewer implementation of this <code>Viewer</code> framework
	 * method ensures that the given label provider is an instance of
	 * <code>ITableLabelProvider</code>, <code>ILabelProvider</code>, or
	 * <code>CellLabelProvider</code>.
	 * <p>
	 * If the label provider is an {@link ITableLabelProvider}, then it
	 * provides a separate label text and image for each column. Implementers of
	 * <code>ITableLabelProvider</code> may also implement
	 * {@link ITableColorProvider} and/or {@link ITableFontProvider} to provide
	 * colors and/or fonts.
	 * </p>
	 * <p>
	 * If the label provider is an <code>ILabelProvider</code>, then it
	 * provides only the label text and image for the first column, and any
	 * remaining columns are blank. Implementers of <code>ILabelProvider</code>
	 * may also implement {@link IColorProvider} and/or {@link IFontProvider} to
	 * provide colors and/or fonts.
	 * </p>
	 * 
	 */
	public void setLabelProvider(IBaseLabelProvider labelProvider) {
		Assert.isTrue(labelProvider instanceof ITableLabelProvider
				|| labelProvider instanceof ILabelProvider
				|| labelProvider instanceof CellLabelProvider);
		updateColumnParts(labelProvider);
		
		super.setLabelProvider(labelProvider);
	}