“Just as proceedings for perjury are available to deal with the witness who would otherwise be protected against statements made in the witness box, so also the public interest requires that a remedy for malicious prosecution should remain available against those who would be entitled to the benefit of the absolute privilege but who have acted maliciously and without reasonable and probable cause during the investigation process. But that is a quite separate matter as it is the malicious abuse of process, not the making of the statement, which provides the cause of action. The public policy argument for extending the absolute privilege, consistently with established principles, seems to me to be unanswerable.”