Stop this Tracer.

def stop(self):
        """
        Stop this Tracer.
        """
        if hasattr(sys, "gettrace") and self.log:
            if sys.gettrace() != self._trace:
                msg = "Trace function changed, measurement is likely wrong: %r"
                print >> sys.stdout, msg % sys.gettrace()
        sys.settrace(None)