Workaround for createFromFormat on PHP > 5.2

Not sure if a new class extending DateTime is the better choice for this, but since DateTime::createFromFormat is only used on two files I think it works fine.

I haven't tested all the cases where it's used, but on those where I test seems to work. On this ( http://3v4l.org/P1Kii ) fiddle it seems to return the same output on all PHP versions > 5.2