Probe branch: Failing test for missing probe.

I noticed that the first initializer in `var b = 2, c = 3` isn't probed. `tracer.traceProbeValue` is actually called but the corresponding nodeId doesn't exist in the list of nodeIds sent to `tracer.add`, so it seems to be dropped.

I saw that you implied work on nodeIds wasn't quite complete, and I'm still working out how Fondue works well enough to contribute a patch, but I was able to at least produce this failing test to demonstrate the problem. I'm offering it as this PR if it's useful to you.