Allow plugins to enchant normally unenchantable items. Adds BUKKIT-1849

It's currently not possible for a plugin to allow enchanting of an
otherwise un-enchantable item using the enchanting table. This commit
causes EnchantItemEvent to be called with an empty list of enchantments,
allowing a plugin to provide it's own set of enchantments when vanilla
Minecraft would not allow any. It also bypasses the unsafe enchantment check
since a plugin should be permitted to apply any enchantments they like, and
vanilla should not generate unsafe enchantments of its own.
Make AnvilInventory.getItem() use both containers. Fixes BUKKIT-2788

The AnvilInventory reports its size as the sum of the ingredient and
result inventories, but when trying to access the slots, only the
ingredient inventory is used, leading to an ArrayIndexOutOfBounds exception.

This change overrides getItem(I) and setItem(I) to use both inventories,
with the slot number adjusted based on their size.
Faux sleepers wake up normally. Fixes BUKKIT-3667