multiple fields : wrong outlined items on validation error

Currently with 'core' CCK fields (text, number, userref, noderef), when a field is multiple, and one of the values fails validation, all the form elements for the field are outlined as "error", instead of just the one that's actually wrong.

This is dealt field module per field module. Contrib modules might have the same bug - Karen's date.module does not :-)

This patch (4.7) deals with text, number and userref - noderef is dealt with in http://drupal.org/node/62498.

This patch also updates "dummy" field.php, in order to give contrib developers a hint :-)