Katy Perry and Britney Spears appear on a CD together but it's not the latest "Now" compilation. Rather, the pop singers have written songs on Selena Gomez & the Scene's new album, "When the Sun Goes Down." "I did have a lot of artists that I was very lucky enough to have songs written by and it's a good, uplifting album," Gomez said of her third CD. "It's really fun and very dance-y and I hope people like it." Spears co-wrote the dance song "Whiplash," while Perry co-penned "That's More...