Bug 156883 [Viewers] enhancements to ILazyTreeContentProvider
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreeViewer.java
* 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);
		clearColumnParts();
		super.setLabelProvider(labelProvider);
	}
	/**
	 * Clear the viewer parts for the columns
	 */
	private void clearColumnParts() {
		TreeColumn[] columns = getTree().getColumns();
		if (columns.length == 0)
			getTree().setData(ViewerColumn.COLUMN_VIEWER_KEY, null);
		else {
			for (int i = 0; i < columns.length; i++) {
				columns[i].setData(ViewerColumn.COLUMN_VIEWER_KEY, null);
			}
		}
	}
	/*
	 * (non-Javadoc) Method declared in AbstractTreeViewer.
	 */
	protected void setSelection(List items) {
		Item[] current = getSelection(getTree());