Description:
------------
When a DateTime is constructed with a non-UTC timezone and one day is added, the 
time also jumps forward by an hour as well.

Test script:
---------------
$ts = new DateTime('@1341115200', new DateTimeZone('America/New_York'));

$dayFromTs = new DateTime('@1341115200', new DateTimeZone('America/New_York'));
$dayFromTs->add(new DateInterval('P1D'));

echo 'ts: '.$ts->format('Y-m-d H:i:s')."\n";
echo 'day from ts: '.$dayFromTs->format('Y-m-d H:i:s')."\n";

Expected result:
----------------
ts: 2012-07-01 04:00:00
day from ts: 2012-07-02 04:00:00

Actual result:
--------------
ts: 2012-07-01 04:00:00
day from ts: 2012-07-02 05:00:00