Justin Timberlake’s gone puss-swapping — he’s supposedly dumping girlfriend of three years Jessica Biel for singer Rihanna. Star Magazine saysAfter a hot grinding session at 1Oak’s MTV Video Music Awards bash in NYC, RiRi and JT moved to her hotel room, where they had a steamy, private after party! “Rihanna and Justin have been talking and texting on the phone nonstop since the VMAs,” said a