Kurio, after solve the problem,
torrent flux is not in Portage. I dont know if exists in Entropy, but if no...
ou may download their souce code and compile, or
you may try an binary for Slackware...
Several slackware packages (for ex, the messenger mercury) runs well ei Gentoo and Sabayon.
althoug Sabayon and Gentoo may accept rpm commands, less chance to work good, using RPM packages ( typically for RedHat, Fedora, Mandriva and OpenSUSE)