CPP13 — Abstract interface and DSI issue with C++

There doens't appear to be any portable way to implement an object that
inherits from an abstract interface using the DSI in C++ without compile
time knowledge of the abstract interface. The basic problem is that I
can create an object reference from a POA, but there is no way to
convert the reference into an abstract interface reference so that I can
send it out on the wire.

We need some mechanism to coerce an object reference into an abstract
interface reference (with a runtime check) to make this work.