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/metadata/ExtendsPropertyType.java
*/
	public ExtendsPropertyType( )
	{
		super( DISPLAY_NAME_KEY );
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.design.metadata.PropertyType#getTypeCode()
	 */
	public int getTypeCode( )
	{
		return EXTENDS_TYPE;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.design.metadata.PropertyType#getXmlName()
	 */
	public String getName( )
	{
		return EXTENDS_TYPE_NAME;
	}
	/**
	 * Validates an extends property value of an element. The value can be a
	 * string value that takes the name of the target element, or it can be the
	 * instance of the target element.
	 * 
	 * @return An <code>ElementRefValue</code> that holds the target element,
	 *         the reference is resolved if the input value is the instance of