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
assert derived.contains( child );
		derived.remove( child );
	}
	/**
	 * Sets the parent element. This version should be used to implement a
	 * command to change the parent element. The caller must have validated that
	 * the new parent is valid for this element.
	 * <p>
	 * Part of: Inheritance system.
	 * 
	 * @param base
	 *            The new parent element, or null if the element is to have no
	 *            base element.
	 */
	public void setExtendsElement( DesignElement base )
	{
		DesignElement oldExtends = getExtendsElement( );
		if ( base == oldExtends )
			return;
		if ( oldExtends != null )
			oldExtends.dropDerived( this );
		if ( base == null )
		{
			extendsRef = null;
		}
		else
		{
			
			assert base.getDefn( ) == getDefn( );