Peter Ackroyd turns his gimlet eye to one of the twentieth century's most revered directors.      Alfred Hitchcock was a strange child. Fat, lonely, burning with fear and ambition, his childhood was an isolated one, scented with fish from his father's shop. How did this fearful figure become the most respected film director of the twentieth century?     Hitch, as he preferred to be called, rigourously controlled the press's portrait of himself, drawing certain carefully-selected childhood anecdotes into full focus, blurring all others out. Peter Ackroyd's new account of his life wrests the director's chair back from the master of control and discovers what lurks just out of sight, in the corner of the shot.