Description:
------------
The DateTime constructor throws an Exception warning that it is not safe to rely 
on the system's timezone settings if you try to construct a DateTime object and 
haven't somehow specified a timezone, whether by using date_default_timezone_set, 
the date.timezone setting, or the $timezone argument of DateTime itself.

However, there is another way to specify the timezone for a DateTime object, by 
passing a time string which includes a timezone as the first argument to the 
constructor. When such a string is given, the $timezone argument is ignored and 
the timezone given in the string is always used.

However, this doesn't prevent the Exception from being thrown, even though a 
timezone is being specified. To avoid the Exception, you have to have a default 
timezone set, or you have to pass a DateTimeZone as the second argument, even 
though neither would actually be used for creating the object.

Test script:
---------------
<?php

ini_set('date.timezone', NULL);

try {
    $date = new DateTime('2011-08-28T00:00:00+0000');
    echo $date->format('O');
} catch (Exception $e) {
    echo 'Exception thrown.';
}

echo PHP_EOL;

date_default_timezone_set('America/New_York');
try {
    $date = new DateTime('2011-08-28T00:00:00+0000');
    echo $date->format('O');
} catch (Exception $e) {
    echo 'Exception thrown.';
}

Expected result:
----------------
+0000
+0000

Actual result:
--------------
Exception thrown.
+0000