[Bleeding] Implementation of inventory framework. Addresses BUKKIT-856

See the corresponding Bukkit commit for details.

Implementation details:
- Any packets that include an itemstack will send air stacks as null; maybe this will even eliminate the client crash that occurs if the client receives an air stack
- Better handling of null itemstacks in general (ie less converting them to air stacks)
- Inventory.setContents() can now take an array smaller than the inventory without error
- Player.updateInventory() should now correctly update the result slot in a crafting inventory

Some small credit goes to Afforess (initial implementation of openInventory() methods) and Drakia (initial implementation of InventoryOpenEvent and InventoryCloseEvent).

src/main/java/net/minecraft/server/IInventory.java

@@ -1,5 +1,13 @@
 package net.minecraft.server;
 
+// CraftBukkit start
+import java.util.List;
+
+import org.bukkit.craftbukkit.entity.CraftHumanEntity;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.inventory.InventoryHolder;
+// CraftBukkit end
+
 public interface IInventory {
 
     int getSize();
@@ -22,5 +30,15 @@ public interface IInventory {
 
     void g();
 
-    public abstract ItemStack[] getContents(); // CraftBukkit
+    // CraftBukkit start
+    ItemStack[] getContents();
+    
+    void onOpen(CraftHumanEntity who);
+    
+    void onClose(CraftHumanEntity who);
+    
+    List<HumanEntity> getViewers();
+    
+    InventoryHolder getOwner();
+    //CraftBukkit end
 }