Make GPLv2 and GPLv3 coexist in the same project?

cyclop writes: "I am coding a data analysis application in my laboratory that I would like to release as free (as in freedom) software. Moreover I am going to begin a small OSS game that will be based, in part, on GPLv2 libraries. Problem is: in both cases, I'd like to be able to exchange code both with GPLv2 and (future) GPLv3 projects. I have no particolar passions about both licences, only thing is I don't want BSD-style "do anything you want" licensing but a copyleft license. I know that GPLv2 and GPLv3 are not compatible. What can I do? Double-licensing? Is there a compatible-with-both licence? Adding exceptions? What do you think is the best way to address the GPLv2-to-GPLv3 transition without ending in one of the two sides of the barricade?"