stop using boost::shared_ptr in pdu::Disseminator::Receiver
Use of boost::shared_ptr<PDU> in pdu::Disseminator::Receiver is cute, but it prevents the declaration of type specific PDU receivers requiring the PDU* to be casted within the receiver.
A better way should be found to remove these limitations.
much better PDU disseminator registration methods that allow non std::shared_ptr wrapped concrete PDU types to be used in handlers while providing compile time type safety. refs #15