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
|| level == DesignElement.SHORT_LABEL
				|| level == DesignElement.FULL_LABEL;
		return getElement( ).getDisplayLabel( module, level );
	}
	/**
	 * Sorts a list of elements by localized display name.
	 * 
	 * @param list
	 *            the list to sort
	 */
	public static void doSort( List list )
	{
		Collections.sort( list, new Comparator( ) {
			public int compare( Object arg0, Object arg1 )
			{
				DesignElementHandle h1 = (DesignElementHandle) arg0;
				DesignElementHandle h2 = (DesignElementHandle) arg1;
				String s1 = h1.getDisplayLabel( );
				String s2 = h2.getDisplayLabel( );
				return s1.compareTo( s2 );
			}
		} );
	}
	/**
	 * Returns whether the element is valid or not. An element may be valid even
	 * though it has some semantic errors.
	 * 
	 * @return <code>true</code> if this element is valid, otherwise
	 *         <code>false</code>.
	 */