Comment on BlockPlacementHandler regarding double-packet behavior

BlockPlacementHandler.java

        /**
         * The client sends this packet for the following cases:
         * Right click air:
         * - Send direction=-1 packet for any non-null item
         * Right click block:
         * - Send packet with all values filled
         * - If client DOES NOT expect a block placement to result:
         *   - Send direction=-1 packet (unless item is null)
         *
         * Client will expect a block placement to result from blocks and from
         * certain items (e.g. sugarcane, sign). We *could* opt to trust the
         * client on this, but the server's view of events (particularly under
         * the Bukkit API, or custom ItemTypes) may differ from the client's.
         *
         * In order to avoid firing two events for one interact, the two
         * packet case must be handled here. Care must also be taken that a
         * right-click air of an expected-place item immediately after is
         * not considered part of the same action.
         */