Description:
------------
I'm testing a snapshot of the current Joomla Platform on PHP 5.4 (unsung Zend 
Server CE) and just met an old friend. We're extending DateTime and would like to 
type hint the $timezone argument in setTimezone().

Sample code:
class JDate extends DateTime
{
    public function setTimezone(DateTimeZone $tz)
    {
        return parent::setTimezone($tz);
    }
}

This causes the following E_STRICT error:
Strict Standards: Declaration of JDate::setTimezone() should be compatible with 
DateTime::setTimezone($timezone)

The issue is not limited to PHP 5.4 but also occurs in older versions.

According to the documentation 
(http://php.net/manual/en/datetime.settimezone.php) the only valid value is a 
DateTimeZone object so it should be type hinted.