Messages tracing

[emil14]

Maybe it has some profit to extend msg interface with Trace() MsgTrace method? So every message will "remember" it's path

Related to #92

[emil14]

This is how it can look like

comp root() {
    _, err = httpget(req)
	if err != nil {
		log(err)
	}
}

httpget(req) {
	err = syscall()
	return req, err
}

syscall {
	err = error("...")
	return err
}

---

root/httpger/syscall/error.err
root/httpger/syscall.err
root/httpger.err
root/log.msg

Problem

Naive implementation will give this result:

root/httpger/syscall/error.err
root/httpger/syscall.err
root/httpger/syscall.err
root/httpger.err
root/httpger.err
root/log.msg

Where we have duplicates because the outport is an inport for internal network

Problem 2 Concurrency

Is it save to append to trace from different places? Looks like trace must always be copied