The guy's had a past, and a substantial one at that: Among his troubles: two warrants for his arrest in Virginia for alleged credit-card theft and fraud; an unpaid $6,087 legal bill, and a $502,910 judgment against him by a British investment firm. And Us Weekly reports in its new issue that Monjack gave his former fiancée, British film producer Taira Rafiq, an engagement ring he had told her was a diamond but was, in fact, cubic zirconia. "Taira tried to get in touch with Brittany to warn her," a Rafiq pal tells Us. Where there's smoke, there's fire. Murphy...