Delay firing EntityInteractEvent until arrow-button collision is confirmed. Fixes BUKKIT-3686

Currently when an arrow hits the same block that contains a wooden button, an EntityInteractEvent is fired even if the button itself isn't actually hit.  This patch fixes it in a sort of strange way, but the only way I could come up with.

Leaky: https://bukkit.atlassian.net/browse/BUKKIT-3686