Description:
------------
date_diff has a problem with a specific date
it doesn't calculate days between two dates correctly
please see the example
( it seems there is a similar problems: http://www.php.net/manual/en/datetime.diff.php#101990 )

Test script:
---------------
$interval = date_diff(date_create('2000-03-21'), date_create('2013-03-21'));
echo $interval->format('%a') . "<br>\n";  // will output 4747


$interval = date_diff(date_create('2000-03-21'), date_create('2013-03-22'));
echo $interval->format('%a') . "<br>\n";  // will output 4749   --- WRONG!


$interval = date_diff(date_create('2000-03-21'), date_create('2013-03-23'));
echo $interval->format('%a') . "<br>\n";  // will output 4749


$interval = date_diff(date_create('2000-03-21'), date_create('2013-03-24'));
echo $interval->format('%a') . "<br>\n";  // will output 4750

Expected result:
----------------
4747
4748
4749
4750


Actual result:
--------------
4747
4749
4749
4750



the second calculation is wrong