Resolve the problem of having to double-enchant launchers and ammo and get double bonuses in one of two ways:

1. Make the double bonuses at higher cost a feature of ammo-based fighting. You can now enchant rocks and flint stones, though all randomly generated ones must be +0.
2. Make ammunition unenchantable (but still fooproofable), and the launcher enchantment affects to-hit and damage bonuses like normal. This is good because it means that ammo stack management is less annoying.