tracer.go
func (t *BTTracer) AddKV(options []string, key, val string) []string {
	return t.AddOptions(options, t.kvp, key+t.kvd+val)
}
func (t *BTTracer) AddKV(options []string, key, val string) []string {
	return t.AddOptions(options, t.kvp, key+t.kvd+val)
}
// See bcd.Tracer.AddKV().