returns the row attribute's value which was set in the 
| rId | string|number | row id | 
| name | string | the attribute's name | 
| mixed | the row attribute's value set in the | 
<?xml version='1.0' encoding='iso-8859-1'?>
    <rows>
        <row id="unique_rowid" some="data">
            <cell some="data">cell content</cell>
        </row>
    </rows>
    ...
var rowAttr = myGrid.getRowAttribute("unique_rowid","some");