In terms of blithely doffing self-respect, Ally McBeal's got nothing on Marlon Brando. In this grossly misguided comedy, the Actor Formerly Regarded as Great is a domineering prison warden prone to shooting would-be escapees, sporting ''Jesus Saves'' in blue ink on the back of his head and falling dome-first into toilets. Add to the cringe-fest a half-baked plot about a train heist and enough dimwit dialogue to shake a stick at. Typical exchange: ''What's going on?'' ''I don't have one hint.'' Neither do we. F