[Bleeding] Fix some inventories not using maxStack. Fixes BUKKIT-2883

CraftBukkit adds the ability to specify the maxStack size for most
inventories. However, some inventories were not overriding the getMaxStack
method properly, and so the functionality was unavailable. This fixes the
maxStack setting for Anvils, Minecarts, PlayerInventory, and Hoppers.

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

@@ -145,7 +145,7 @@ public abstract class EntityMinecartContainer extends EntityMinecartAbstract imp
     }
 
     public int getMaxStackSize() {
-        return 64;
+        return maxStack; // CraftBukkit
     }
 
     public void b(int i) {