Fix infinite 'breeding' with MonsterEggs. Fixes BUKKIT-2997

If the player is not in Creative (i.e. does not have the ability to
instantly build) we need to decrement the MonsterEgg item stack when used
on a breedable parent mob.

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

@@ -22,6 +22,12 @@ public abstract class EntityAgeable extends EntityCreature {
                     entityageable.setAge(-24000);
                     entityageable.setPositionRotation(this.locX, this.locY, this.locZ, 0.0F, 0.0F);
                     this.world.addEntity(entityageable);
+
+                    // CraftBukkit start
+                    if (!entityhuman.abilities.canInstantlyBuild) {
+                        itemstack.count--;
+                    }
+                    // CraftBukkit end
                 }
             }
         }