Bug 188578 Add "displayColumnName" on TabularLevel
Add Property "displayColumnName" on TabbularLevel and corresponding APIs on handle. Property Type: expression.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/writer/ModuleWriter.java
*/
	protected void writeStructure( DesignElement obj, String propName )
	{
		PropertyDefn prop = (ElementPropertyDefn) obj.getDefn( ).getProperty(
				propName );
		if ( prop == null )
			return;
		IStructure struct = (IStructure) obj.getLocalProperty( getModule( ),
				propName );
		if ( struct == null )
			return;
		writer.conditionalStartElement( DesignSchemaConstants.STRUCTURE_TAG );
		writer.attribute( DesignSchemaConstants.NAME_ATTRIB, propName );
		IStructureDefn structDefn = prop.getStructDefn( );
		Iterator iter = structDefn.propertiesIterator( );
		while ( iter.hasNext( ) )
		{
			StructPropertyDefn strcutPropDefn = (StructPropertyDefn) iter
					.next( );
			
			
			writeMember( struct, strcutPropDefn );
		}
		writer.endElement( );
	}
	/**
	 * Write property or structure according to definition.
	 * 
	 * @param struct
	 *            parent structure.