accessify throw new ErrorException to PHP >= 5.3 only

since 5.2.x (sometimes?) may create strange errors, see http://board.s9y.org/viewtopic.php?f=10&t=19436

I think we don't need to upport this to 2.0, since we will need to bump Serendipity's PHP version to need 5.3 or even up, because of namespaces, security and others soon. PHP 5.2 support has stopped and the PHP 5.3 series has reached end-of-life this summer and will receive only security fixes for the next year.