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
}
		return displayLabel;
	}
	/**
	 * Generates a clone copy of this element. When a report element is cloned,
	 * the basic principle is just copying the property value into the clone,
	 * the other things, like container references, child list references,
	 * listener references will not be cloned; that is, the clone is isolated
	 * from the design tree until it is added into a target design tree.
	 * 
	 * <p>
	 * When inserting the cloned element into the design tree, user needs to
	 * care about the element name confliction; that is, the client needs to
	 * call the method
	 * <code>{@link ReportDesignHandle#rename( DesignElementHandle )}</code>
	 * to change the element names.
	 * 
	 * @return Object the cloned design element.
	 * @throws CloneNotSupportedException
	 *             if clone is not supported.
	 * 
	 */
	public Object clone( ) throws CloneNotSupportedException
	{
		DesignElement element = (DesignElement) super.clone( );
		element.container = null;
		element.listeners = null;
		element.derived = null;
		element.extendsRef = null;
		element.cachedDefn = null;