This method returns a userdata holding the IUnknown interface
pointer to the COM object behind luacom_obj. It's important
to notice that Lua does not duplicates userdata: many calls to
GetIUnknown for the same LuaCOM object will return
the same userdata. This means that the reference count for the
IUnknown interface will be incremented only once (that is, the
first time the userdata is pushed) and will be decremented only when
all the references to that userdata go out of scope (that is, when the
userdata suffers garbage collection).
One possible use for this method is to check whether two LuaCOM
objects reference the same COM object.
Vinicius da Silva Almendra