Add content_extra_fields to allow users to position the node_invite form

CCK has a hook_content_extra_fields() hook that allows you to give weights to specific form areas. Currently there's no way to control /where/ on the form the 'node_invite_group' fieldset will be placed, using this hook will allow you to configure that on the admin/content/node-type//fields page similar to the Menu, Revision, and Path fieldsets.

The following function just needs to be added to node_invite.module:

/**
 * Implementation of hook_content_extra_fields().
 */
function node_invite_content_extra_fields($type_name) {
  $extra = array();
  if (_node_invite_type_is_allowed($type_name)) {
    $extra['node_invite_group'] = array(
      'label' => t('Node invite settings'),
      'description' => t('Node invite module form.'),
      'weight' => 10,
    );
  }
  return $extra;
}