No, joost is referring to Portage 'slots'. In Portage it is possible to have two different versions of the same package installed simultaneously. For example, I have both cnijfilter-3.20-r1 for my Canon MP560 printer and cnijfilter-3.70-r3 for my Canon MP510 printer. The message you are seeing originates from the Portage ebuild that was built by the Entropy repository maintainer and put in the Entropy repository. You don't need to worry about it, as slot changes (usually) are sorted out automatically for you in Entropy due to its 'rolling' upgrade nature.