[Reviewer: Graeme] Live test fixes

Graeme,

Please can you review my fixes coming out of live test with OpenIMSCore HSS?  The changes are

*   being a little less pedantic about result codes and experimental result codes
*   not passing `NULL` to `Diameter::Message::send()` as this segfaults - since the timeout doesn't matter, we don't pass any parameters

I've live-tested this and run the existing UTs (you're still adding UT for this function, so I haven't added any myself).

Thanks,

Matt