Bug 182895 Support sort on Level attribute.
Currently in OLAP engine we only support sort on level key value. We should go ahead to support sort on level attribute value.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/olap/data/impl/aggregation/sort/AggregationSortHelper.java
* 
	 * @return
	 */
	public boolean next( )
	{
		this.index++;
		if ( this.array.size( ) <= this.index )
		{
			this.index = this.array.size( );
			return false;
		}
		return true;
	}
	/**
	 * 
	 * @return
	 * @throws IOException
	 */
	public IAggregationResultRow getCurrentRow( ) throws IOException
	{
		if ( this.index >= this.array.size( ) )
			return null;
		return (IAggregationResultRow) this.array.get( this.index );
	}
}
/**
 * 
 *
 */
class WrapperedDiskArray implements IDiskArray