IT'S hard to believe those gentle, playful dolphins we all love are actually ultra-horny, dangerously jealous creatures - but Jessica Alba and Susan Sarandon can tell you it's true from personal experience. Alba learned just how sex-crazed the lovable mammals are when she filmed the 1990s "Flipper" remake. "Dolphins get excited, even when you are a human being and they have long, long," the "Sin City" hottie told MTV. ". . . I didn't know this until I was being poked by a few of them, which was very rude. I sort of requested female dolphins after that because those...