Description:
------------
Calling "modify()" with a delta of 0 should not change the time, regardless of whether a time zone was defined for the DateTime object or not, and independent from how the object was created (from a UNIX timestamp or a date/time string with or without time zone).


Test script:
---------------
See long version with more details and possible regressions here: http://pastebin.com/v8RybhVh

Below is a short excerpt for the current bug.

<?php
  echo "FROM TIMESTAMP, NO TZ:\n";

  $date = new DateTime('@'.strtotime('2012-08-22 00:00:00 CEST'));
  echo $date->format('Y-m-d H:i:s T').' (offset '.$date->getOffset().")\n";

  $date->modify('+0 days');
  echo $date->format('Y-m-d H:i:s T').' (offset '.$date->getOffset().")\n";
?>


Expected result:
----------------
FROM TIMESTAMP, NO TZ:
2012-08-21 22:00:00 GMT+0000 (offset 0)  <-- should be equal
2012-08-21 22:00:00 GMT+0000 (offset 0)  <-- to this
FROM TIMESTAMP, WITH TZ:
2012-08-22 00:00:00 CEST (offset 7200)
2012-08-22 00:00:00 CEST (offset 7200)
FROM STRING:
2012-08-22 00:00:00 CEST (offset 7200)
2012-08-22 00:00:00 CEST (offset 7200)


Actual result:
--------------
Output from PHP 5.4.4, 5.4.6 and snapshot r4e56105 from August 22, 2012:

FROM TIMESTAMP, NO TZ:
2012-08-21 22:00:00 GMT+0000 (offset 0)  <-- different 
2012-08-21 23:00:00 GMT+0000 (offset 0)  <-- from this
FROM TIMESTAMP, WITH TZ:
2012-08-22 00:00:00 CEST (offset 7200)
2012-08-22 00:00:00 CEST (offset 7200)
FROM STRING:
2012-08-22 00:00:00 CEST (offset 7200)
2012-08-22 00:00:00 CEST (offset 7200)

In PHP 5.2.0, the bug appears when creating DateTime from a string (with time zone), which one might test as well to guard against similar bugs:

FROM TIMESTAMP, NO TZ:
2012-08-21 22:00:00 GMT+0100 (offset 7200)
2012-08-21 22:00:00 GMT+0100 (offset 7200)
FROM TIMESTAMP, WITH TZ:
2012-08-22 00:00:00 CEST (offset 7200)
2012-08-22 00:00:00 CEST (offset 7200)
FROM STRING:
2012-08-22 00:00:00 CEST (offset 7200)  <-- different
2012-08-21 23:00:00 CEST (offset 7200)  <-- from this