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
* property is unresolved. Otherwise, it's cleared.
	 * 
	 * @param referred
	 *            the element to be deleted
	 * @param unresolveReference
	 *            the flag indicating the reference property should be
	 *            unresolved, instead of cleared
	 * @throws SemanticException
	 *             if an error occurs, but the operation should not fail under
	 *             normal conditions
	 * 
	 * @see #adjustReferredClients(DesignElement)
	 */
	private void adjustReferenceClients( ReferenceableElement referred,
			boolean unresolveReference ) throws SemanticException
	{
		List clients = new ArrayList( referred.getClientList( ) );
		Iterator iter = clients.iterator( );
		while ( iter.hasNext( ) )
		{
			BackRef ref = (BackRef) iter.next( );
			DesignElement client = ref.element;
			if ( unresolveReference )
			{
				BackRefRecord record = new ElementBackRefRecord( module,
						referred, client, ref.propName );
				getActivityStack( ).execute( record );
			}
			else
			{