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
* 
 * Design elements maintain a wide variety of relationships to other parts of
 * the design. An element refers to its parent element or its shared style.
 * Expressions reference elements, parameters and data set columns. Many
 * elements reference data sources or data sets.
 * <p>
 * <em>Semantic processing</em> resolves name references to the actual
 * elements or other objects. Semantic processing is done incrementally for most
 * operations. However, batch processing is needed when reading a design file
 * and for certain other operations.
 * <p>
 * Semantic processing is done by doing a depth-first traversal of the design
 * tree. Errors are gathered on the design context.
 * <p>
 * The result of semantic processing may be that the design caches a reference
 * to another element as is done in this class for the parent element and the
 * shared style. In other cases, the reference is checked and then discarded.
 * <p>
 * When a reference is cached, the system must handle the case of a reference
 * that cannot be resolved. For example, an element might use a shared style
 * defined in a template, but that shared style has been deleted from the
 * template and can no longer be resolved. In this case, we cache the name until
 * the user loads the required elements, or changes the reference to an existing
 * style. Similar rules apply to the "extends" property.
 * 
 * @see ElementDefn
 * @see DesignElementHandle
 * @see ElementPropertyDefn
 */
public abstract class DesignElement