code: function isError(error) {
      return error && (Object.prototype.toString.call(error).slice(8, -1) === "Error" ||
          (typeof error.stack !== "undefined" && typeof error.name !== "undefined"));
  }
docs: Determine if a given parameter is an Error.
  
  @method isError
  @private
  @param {Error} error the prospective Error
  @return {Boolean} true is 'error' is an Error; false otherwise