Bug 124620 Referenced Parameter icon should be invalid if the parameter in library is deleted
Description: Referenced parameter icon should be invalid if the source parameter in library is deleted. Steps to reproduce: 1.Create a library. Insert a report scalar parameter. 2.Create a report, use the above library. In the library explorer, pull the parameter to the data explorer view of report. 3.Open the library file, delete the parameter. Then reopen the report design file, the icon of parameter seems nothing happened. But if those operations happened in dataset, the icon of dataset in the report will be invalid. It is acceptable. Expected Result: The icon of referenced parameter should be invalid.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
*/
	public IElementDefn getDefn( )
	{
		if ( cachedDefn == null )
		{
			cachedDefn = MetaDataDictionary.getInstance( ).getElement(
					getElementName( ) );
			assert cachedDefn != null;
		}
		return cachedDefn;
	}
	/**
	 * Adds a user-defined property. The property must be unique within the
	 * inheritance hierarchy of this element. It cannot duplicate either another
	 * user-defined property or a system-defined property. These checks must
	 * have been enforced by the application prior to calling this method.
	 * <p>
	 * Part of: User-defined property system.
	 * 
	 * @param userProp
	 *            definition of the user-defined property
	 */
	public void addUserPropertyDefn( UserPropertyDefn userProp )
	{
		assert getDefn( ).allowsUserProperties( );
		assert userProp != null;
		String propName = userProp.getName( );
		assert getUserPropertyDefn( propName ) == null;
		assert getDefn( ).getProperty( propName ) == null;
		if ( userProperties == null )