add $withDefaultValue param, to omit strict notice

I got this strict notice on my system:

Strict Notice: Declaration of AvS_FastSimpleImport_Model_Import_Entity_Product_Type_Simple::prepareAttributesForSave() should be compatible with Mage_ImportExport_Model_Import_Entity_Product_Type_Abstract::prepareAttributesForSave(array $rowData, $withDefaultValue = true) in foobar\app\code\community\AvS\FastSimpleImport\Model\Import\Entity\Product\Type\Simple.php on line 13