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
* 
	 * @return a style handle to work with the style properties of this element.
	 *         Returns <code>null</code> if this element does not have style
	 *         properties.
	 */
	public StyleHandle getPrivateStyle( )
	{
		if ( getDefn( ).hasStyle( ) )
			return new PrivateStyleHandle( module, getElement( ) );
		return null;
	}
	/**
	 * Returns the name of this element. Returns <code>null</code> if the
	 * element does not have a name. Many elements do not require a name. The
	 * name does not inherit. If this element does not have a name, it will not
	 * inherit the name of its parent element.
	 * 
	 * @return the element name, or null if the name is not set
	 */
	public String getName( )
	{
		return getElement( ).getName( );
	}
	/**
	 * Gets the name of this element. The returned element name will be the same
	 * as <CODE>getName()</CODE>, plus the namespace of the module that the
	 * elment is contained, if any. If the element is existed in the current
	 * module,this method and <CODE>getName()</CODE> will return identical
	 * results.
	 *