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
* (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.core.IPropertySet#setProperty(org.eclipse.birt.report.model.metadata.PropertyDefn,
	 *      java.lang.Object)
	 */
	public void setProperty( PropertyDefn prop, Object value )
	{
		setProperty( (ElementPropertyDefn) prop, value );
	}
	/**
	 * Clears the local value of the property. See <code>setProperty( )</code>
	 * for details. This is equivalent to calling
	 * <code>setProperty( propName, null )</code>.
	 * <p>
	 * Part of: Property value system.
	 * 
	 * @param propName
	 *            The name of the property to set. Must be valid. Can be a
	 *            system-defined or user-defined property name.
	 */
	public void clearProperty( String propName )
	{
		setProperty( propName, null );
	}
	/**
	 * Returns the definition object for this element.
	 * <p>
	 * Part of: Meta data system.
	 * 
	 * @return The element definition. Will always be non-null in a valid build.