Bug 183910 Cross tab can not be reverted to template item after it is reverted to report item [1102]
Description: Cross tab can not be reverted to template item after it is reverted to report item. Build number: 2.2.0.v20070425-0630 Steps to reproduce: 1. New a cross tab. 2. Right click to select the cross tab, choose "Create Template Report Item" to create template item, then revert the cross tab to report item. 3. Right click to select the cross tab. Expected result: The cross tab cna be revert to report item and template item both. Actual result: In the context menu, "Revert To Report Item" and "Revert To Template Item" are grayed out. Error log: N/A
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/ContentCommand.java
* then adds it to the container here. The undo of this operation
	 * effectively deletes the element.
	 * 
	 * @param content
	 *            the element to add
	 * @param slotID
	 *            the slot in which to add the component
	 * @param newPos
	 *            the position index at which the content to be inserted. If
	 *            it's -1, the content will be inserted at the end of the slot.
	 * @throws ContentException
	 *             if the content cannot be added into this container.
	 * @throws NameException
	 *             if the name of the content exists in name space.
	 */
	protected void checkBeforeAdd( DesignElement content )
			throws ContentException, NameException
	{
		assert content.getContainer( ) == null;
		super.checkBeforeAdd( content );
		
		
		if ( element.isVirtualElement( ) || element.getExtendsName( ) != null )
			throw ContentExceptionFactory
					.createContentException(
							focus,
							content,
							ContentException.DESIGN_EXCEPTION_STRUCTURE_CHANGE_FORBIDDEN );
		if ( focus.getSlotID( ) == IModuleModel.COMPONENT_SLOT )
		{