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
* @throws ExtendsException
	 *             if an error occurs, but the operation should not fail under
	 *             normal conditions
	 */
	private void adjustDerived( DesignElement obj ) throws ExtendsException
	{
		
		Collection derived = obj.getDerived( );
		if ( derived.isEmpty( ) )
			return;
		DesignElement parent = obj.getExtendsElement( );
		Iterator iter = derived.iterator( );
		while ( iter.hasNext( ) )
		{
			DesignElement child = (DesignElement) iter.next( );
			ExtendsCommand childCmd = new ExtendsCommand( module, child );
			childCmd.setExtendsElement( parent );
		}
	}
	/**
	 * Adjusts references to an element that is to be deleted. The element to be
	 * deleted is one that has references in the form of element reference
	 * properties on other elements. These other elements, called "clients",
	 * each contain a property of type element reference and that property
	 * refers to this element. Each reference is recorded with a "back pointer"
	 * from the referenced element to the client. That back pointer has both a
	 * pointer to the client element, and the property within that element that
	 * holds the reference. There are two algorithms to handle this reference
	 * property, which can be selected by <code>unresolveReference</code>. If
	 * <code>unresolveReference</code> is <code>true</code>, the reference