What is the way to add additional fields to attachments in 3.5+?

I used to use attachment_fields_to_edit filter, but it seems that in 3.5+ it has been dropped. What is the new way of adding additional attachment fields?

UPDATE:

It seems that it wasn’t dropped, but – deprecated. In 3.6 it operates in compatibility mode. To make a new field appear in media popup, one should set additional param – show_in_modal to true (helpful post here):

$form_fields['thumb-url'] = array(
    'label' => __('Thumbnail Url'),
    'input' => 'html',
    'html'  => <p> ... some html here ... </p>,
    'show_in_modal' => true // <- this one
);

But – still, the whole thing is deprecated and doomed to be dropped sooner or later. There should be a new way of doing things. Anyone knows what that’d be?