function _fnNodeToColumnIndex( oSettings, iRow, n )
	{
		return $.inArray( n, oSettings.aoData[ iRow ].anCells );
	}
Take a TD element and convert it into a column data index (not the visible index)
 @param {object} oSettings dataTables settings object
 @param {int} iRow The row number the TD/TH can be found in
 @param {node} n The TD/TH element to find
 @returns {int} index if the node is found, -1 if not
 @memberof DataTable#oApi