Los Angeles police are asking for the public's help in locating a man who was convicted of threatening to kill pop icon Madonna.  54 year-old Robert Dewey Hoskins was convicted on several charges in 1996 after he tried to break into Madonna's Hollywood Hills home, where the singer's personnel security shot the man.  Hoskins reportedly left the state mental hospital he was comitted to last Friday, and authorities have been unable to locate him.  The man is considered "highy psychotic" and possibly dangerous, and police are asking anyone who sees him to contact the authorities immediately.