Waterproof

Basically this prevents ***holes from placing water buckets on End portals to destroy them. It also special-cases Nether portals so existing Redstone circuits which employ buckets to disable them will still work.

This could be probably fixed on the Bukkit side using a plugin, but I feel that being able to break a block as hard as bedrock by placing a water bucket is a bug and should be fixed on the NMS side.