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 writeContents( DesignElement obj, int slot, String tag )
	{
		writeContents( new ContainerContext( obj, slot ), tag );
	}
	/**
	 * Writes the contents of an element property. The contents are enclosed in
	 * an optional list tag.
	 * 
	 * @param obj
	 *            the container element
	 * @param propName
	 *            the element property to write
	 * @param tag
	 *            the optional list tag that encloses the list of contents
	 */
	protected void writeContents( DesignElement obj, String propName )
	{
		writeContents( new ContainerContext( obj, propName ),
				DesignSchemaConstants.PROPERTY_TAG );
	}
	/**
	 * Writes the contents of a slot. The order is not the order in the slot
	 * while we first write the ancestor and then the derived ones. The contents
	 * are enclosed in an optional list tag.
	 * 
	 * @param obj
	 *            the container element
	 * @param slot
	 *            the slot to write
	 * @param tag