Appends an arbitrary Object to the message. The object
will be encoded in a binary field, using the standard serialization
mechanism. Therefore, the object passed to this method must
implement the Serializable interface. Note that any objects to
be serialized must not only themselves be implemented as Serializable,
but all of the classes they extend must be Serializable.
This object will only be useful to receiving clients in .NET, C/C++/Java
clients will receive a binary field which may be forwarded to
other .NET clients.