PHP Bug 52854

This test verifies we're not affected by [PHP Bug 52854](https://bugs.php.net/bug.php?id=52854). See xp-framework/core#5 - this issue exists in XP 6.0.0 due to a refactoring applied to generics. It remains to be discussed whether we should drop PHP 5.3 support, so this might no longer need a workaround there.