Merge changes from bukkit

Currently there is a bug in bukkit with plock placevent where modifying the itemstack currently being placed does not currently update the itemstack.  Here is the fix in craftbukkit: https://github.com/Bukkit/CraftBukkit-Bleeding/commit/586b704182947a2a0a195fc0004f83b7201fea09#commitcomment-7398500 .  I am posting this here and doing the changes  because I was hoping that spigot would merge it since it is taking bukkit a long time to merge this.  I've tested this and it works.