#10 Uses depecated session_is_registered()

[Paul Robinson]

Under version 5.2 of PHP, the following error message is reported:

Deprecated: Function session_is_registered() is deprecated in /f2/paulrobinson/public/iwebcal/class/iWebCal.inc on line 103

This code reads as
if ($new_session = !session_is_registered("stored_calendar")) {

According to comments at PHP.NET
http://php.net/manual/en/function.session-is-registered.php
this line should be changed to:
if ($new_session = ! (isset($_SESSION["stored_calendar"]))) {