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/api/DesignElementHandle.java
* @see #getFloatProperty
	 * @see #getNumberProperty
	 */
	public Object getProperty( String propName )
	{
		
		DesignElement element = getElement( );
		Object value = element.getProperty( module, propName );
		if ( value instanceof ReferenceValue )
			return ReferenceValueUtil.needTheNamespacePrefix(
					(ReferenceValue) value, getModule( ) );
		return value;
	}
	/**
	 * Returns the value of a property as a string which is locale independent.
	 * 
	 * @param propName
	 *            the name of the property
	 * @return the internal string property value of the property.
	 */
	public String getStringProperty( String propName )
	{
		return getElement( ).getStringProperty( module, propName );
	}
	/**
	 * Return a localized string version of the property. This method will works
	 * for all property types except a list. Dates and numbers will be converted
	 * using the current locale. Display name will be returned for a choice or a
	 * color property.
	 *