Description:
------------
PHP will accept invalid DST-related time zone abbreviations, e.g. daylight 
savings time when daylight savings time cannot be in effect on the given date; 
subsequent operations on the returned object may produce invalid results.

This should produce an error.

Test script:
---------------
        $dt = new DateTime('1980-01-01 15:00:00 PDT');
        print_r($dt);
        $dt->modify('+1 hour');
        print_r($dt);


Expected result:
----------------
EXPECTED output should be an error.


Actual result:
--------------
DateTime Object
(
    [date] => 1980-01-01 15:00:00
    [timezone_type] => 2
    [timezone] => PDT
)
DateTime Object
(
    [date] => 1980-01-01 15:00:00
    [timezone_type] => 2
    [timezone] => PDT
)


Note that PDT is invalid for the given date, and the modify() call didn't work 
and also didn't throw an error.