Added item-in-hand related API.

src/main/java/org/bukkit/craftbukkit/entity/CraftHumanEntity.java

@@ -40,6 +40,10 @@ public class CraftHumanEntity extends CraftLivingEntity implements HumanEntity {
         return getInventory().getItemInHand();
     }
 
+    public void setItemInHand(ItemStack item) {
+        getInventory().setItemInHand(item);
+    }
+
     @Override
     public String toString() {
         return "CraftHumanEntity{" + "id=" + getEntityId() + "name=" + getName() + '}';

src/main/java/org/bukkit/craftbukkit/inventory/CraftInventoryPlayer.java

@@ -22,6 +22,14 @@ public class CraftInventoryPlayer extends CraftInventory implements PlayerInvent
         return new CraftItemStack( getInventory().e() );
     }
 
+    public void setItemInHand(ItemStack stack) {
+        setItem( getHeldItemSlot(), stack );
+    }
+
+    public int getHeldItemSlot() {
+        return getInventory().c;
+    }
+
     public CraftItemStack getHelmet() {
         return getItem( getSize() + 0 );
     }