Before swing came, Betty Boop product of the jazz age, did all right. She was animated "hot stuff" with her curls and bangs, ear-rings, bracelets and curves. But then, like a Hollywood glamour girl who has to change her type to save her career,  Betty met the challenge of a new era. She put away flapperish things and changed her personality. No longer is she old-fashioned. After Max Fleischer's artists revamped her, Betty Boop gradually became a new person.  She lost most of her curls, the part in her hair and jewelry. Like a real actress, she's careful not to show her profile, which doesn't flatter her. She dresses more modestly, too - and she wants you to take her as a streamlined swingtime miss in the modern tempo.