Show assignment due dates in Calendar view (calendar/date module support)

I would like to be able to show assignments by due date in my Calendar module view. However the Calendar module only displays date fields that are registered via hook_date_api_fields().

Looking at the CVS repository it appears that the code is being reorganized, and the file I modified to add this support (gradebookapi.views.inc) has been removed. So rather than providing a diff, here is the code necessary to allow the Calendar module to display assignments by due date:

/**
 * Implementation of hook_views_data().
 */
function gradebookapi_views_data()  {
  $data = array();
  $data['gradebookapi_assignment']['table']['group']  = t('Gradebook Assignment');

  // tables + fields that can be used for SQL Joins
  $data['gradebookapi_assignment']['table']['join'] = array(
    'node' => array(
      'left_field' => 'nid',
      'field' => 'nid',
    ),
  );

  $data['gradebookapi_assignment']['due_date'] = array(
    'title' => t('Due Date'),
    'help' => t('Date on which the Gradebook Assignment is due.'),
    'field' => array(
      'handler' => 'views_handler_field_date',
      'click sortable' => TRUE,
    ),
    'filter' => array(
      'handler' => 'views_handler_filter_date',
    ),
    'sort' => array(
      'handler' => 'views_handler_sort',
    ),
  );

  $data['gradebookapi_assignment']['publish_date'] = array(
    'title' => t('Publish Date'),
    'help' => t('Date on which the Gradebook Assignment was published.'),
    'field' => array(
      'handler' => 'views_handler_field_date',
      'click sortable' => TRUE,
    ),
    'filter' => array(
      'handler' => 'views_handler_filter_date',
    ),
    'sort' => array(
      'handler' => 'views_handler_sort',
    ),
  );
  
  return $data;
}

/**
 * Implementation of hook_date_api_fields().
 */
function gradebookapi_date_api_fields($field) {
  if ($field == 'gradebookapi_assignment.publish_date') {
    return array(
      'sql_type' => DATE_UNIX, // DATE_ISO or DATE_UNIX or DATE_DATETIME
      'tz_handling' => 'site', // 'site' or 'none' or 'date' or 'utc'
    );
  }
  if ($field == 'gradebookapi_assignment.due_date') {
    return array(
      'sql_type' => DATE_UNIX, // DATE_ISO or DATE_UNIX or DATE_DATETIME
      'tz_handling' => 'site', // 'site' or 'none' or 'date' or 'utc'
    );
  }
}