Bug 154828 Item from library contant user properties can't delete
Details: Item from library contant user properties can't delete Step: 1.New a library. 2.Add a label and add a user properites. 3.Public the library. 4.New a report design and use the library 5.Drop the label from library explorer into layout. 6.Try to delete it. Actual result: The label from library contant user properties can't be delete. Exception reuslt: The label can be delete.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/ContentCommand.java
* @param toSlotID
	 *            the slot within the new container.
	 * @param newPos
	 *            the position in the target slot to which the content will be
	 *            moved. If it is -1 or greater than the size of the target
	 *            slot, the content will be appended at the end of the slot.
	 * @throws ContentException
	 *             if the content cannot be moved to new container.
	 */
	private void doMove( DesignElement content, int fromSlotID,
			DesignElement to, int toSlotID, int newPos )
			throws ContentException
	{
		assert content != null;
		assert to != null;
		assert newPos >= -1;
		
		if ( element == to && fromSlotID == toSlotID )
			return;
		
		
		if ( content.isVirtualElement( ) || content.getExtendsName( ) != null )
			throw new ContentException(
					element,
					fromSlotID,
					content,
					ContentException.DESIGN_EXCEPTION_STRUCTURE_CHANGE_FORBIDDEN );
		
		if ( to.isContentOf( content ) )
			throw new ContentException( to, fromSlotID, content,