Description:
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DateTime->setTimezone() is very slow on dates in the far future (or history), and the time needed isnt monotonic for greater dates.

ie. setTimezone() on a DateTime(PHP_INT_MAX) /* 64 bit max */ takes 0.05 seconds, but takes 250 whole seconds for PHP_INT_MAX/2 .

Using the $timezone parameter of the DateTime constructor is always fast though.

Test script:
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	$start = microtime(1);
	$date = new DateTime('@'.(PHP_INT_MAX));
//	$date = new DateTime('@'.(int)(PHP_INT_MAX / 2));
	$date->setTimezone(new DateTimeZone('Europe/Amsterdam'));

	echo microtime(1) - $start;

Expected result:
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A faster change of the timezone; performance equal to using the constructor parameter