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
*         {@link DesignElement#NO_SLOT}if the element is not contained in
	 *         this element.
	 */
	public int findContentSlot( DesignElementHandle content )
	{
		if ( content.getContainer( ).getElement( ) == getElement( ) )
			return content.getElement( ).getContainerSlot( );
		return DesignElement.NO_SLOT;
	}
	/**
	 * Returns the a handle the the container's slot that holds this element.
	 * 
	 * @return the slot handle in which this element resides, <code>null</code>
	 *         if this element has no container.
	 */
	public SlotHandle getContainerSlotHandle( )
	{
		DesignElementHandle containerHandle = getContainer( );
		if ( containerHandle == null )
			return null;
		int slotID = containerHandle.findContentSlot( this );
		assert slotID != DesignElement.NO_SLOT;
		return containerHandle.getSlot( slotID );
	}
	/**
	 * Returns a handle to the given slot. If this element has no such slot,
	 * <code>null</code> will be returned.
	 * 
	 * @param slotID
	 *            the identifier of the slot for which to obtain a handle