Description:
------------
The formatting of the hour offset in date_format()/DateTime->format() differs from the one in date().
Both are correct according to the ISO-8601 specification, though I would expect a consistent format.

Test script:
---------------
date_default_timezone_set("Europe/Amsterdam");
$timeStamp = 1276592400;
$dateTest = new DateTime(date('c', $timeStamp));
echo $dateTest->format(DateTime::ISO8601) ."\n";
echo date_format($dateTest, DateTime::ISO8601)."\n";
echo date('c', $timeStamp) ."\n";

Expected result:
----------------
EITHER
1276592400
2010-06-15T11:00:00+0200
2010-06-15T11:00:00+0200
2010-06-15T11:00:00+0200

OR
1276592400
2010-06-15T11:00:00+02:00
2010-06-15T11:00:00+02:00
2010-06-15T11:00:00+02:00

Actual result:
--------------
1276592400
2010-06-15T11:00:00+0200
2010-06-15T11:00:00+0200
2010-06-15T11:00:00+02:00