Fix bug - hasMany field validation errors not displayed.

[shacky]

If there is a validation error with any of fields in form hasMany field changes keys of new rows from "new_X" to "new__LA_KEY_". This way no validation error is displayed and on the second submit a couple of rows will be merged to one because every new row has the same key: "new__LA_KEY_".

Sample form code:

$form->text('some_required_field')->rules('required');
$form->hasMany('some_relation','Relation',function($form) {
  $form->text('some_relation_required_field')->rules('required');  
});

Now if you left any of this fields empty, form won't validate.
some_relation_required_field will change input name from some_relation_required_field[new_1] to some_relation_required_field[new__LA_KEY_].
If you left some_relation_required_field empty error won't be displayed, because form input name has changed.

Pull request resolves this issue. It's not very elegant, but I couldn't find another way to fix this issue.

[shacky]

It fixes issues #4758 and #4612

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[emacaste]

@z-song why did you not merge this pr? It solves well a very annoyng bug.
Right now the only solution is to extend the base hasMany field