code: function validateBulkGetSupport(db, callback) {
    db.head('_bulk_get',
      function(err) {
        err = error.convertResponseError(err, function(err) {
          switch (err.statusCode) {
            case undefined:
              // There was no status code on the error
              return err;
            case 404:
              return new error.BackupError('BulkGetError', 'Database does not support /_bulk_get endpoint');
            case 405:
              // => supports /_bulk_get endpoint
              return;
            default:
              return new error.HTTPError(err);
          }
        });
        callback(err);
      });
  }
docs: Validate /_bulk_get support for a specified database.
  
  @param {string} db - nodejs-cloudant db
  @param {function} callback - called on completion with signature (err)