HOUSTON, Tex. (AP) -Houston socialite Candace Mossier Garrison and her nephew, Melvin Lane Powers, must pay lawyer Percy Foreman $390,700 for his defense of the two before and during a 1966 murder trial.Powers and Mrs. Garrison were tried in Miami, Fla., in 1966 in the death of Mrs. Garrison’s husband, millionaire Jacques Mossier. They were found innocent. * jState District Court Judge John L. Compton ruled Tuesday that the two still owed Fore- i man $140,000 of a $250,000 fee for defending Powers at the trial. He also ruled that Mrs. iGarrison, who married Houston