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/driver/DimensionAxis.java
/**
	 * Moves cursor to previous row. Return false if the previous row does not
	 * exist
	 * 
	 * @return
	 * @throws OLAPException
	 */
	public boolean previous( ) throws OLAPException
	{
		return this.edgeInfo.dim_previous( dimAxisIndex );
	}
	/**
	 * Moves cursor offset positions relative to current. Returns false if the
	 * indicated position does not exist
	 * 
	 * @param arg0
	 * @return
	 * @throws OLAPException
	 */
	public boolean relative( int arg0 ) throws OLAPException
	{
		return this.edgeInfo.dim_relative( arg0, dimAxisIndex );
	}
	/**
	 * Moves the cursor to the first row in the result set. Returns false if the
	 * result set is empty.
	 * 
	 * @return
	 * @throws OLAPException
	 */