Someone added BitTornado to the portage tree as if it were a new package, but it is a name change (and reversioning) from BitTorrent-TheSHAD0W (bittorrent-theshadow) and should be an upgrade from it.
Hey Luke-Jr, catch me on IM if you have time to chat ;) Anyways, we recently noticed this and are in the process of moving a few packages back to the control of the net-p2p herd, and we'll be doing a bit of restructuring tomorrow (I have been out all weekend and just got back, but don't have time to make any commits tonight). Thanks for filing a bug on it, hopefully everything will be moving smoothly by tomorrow night :).
fixed in portage :-D, thanks!
Luke-Jr pointed out some errors in my idea, so I'm reopening this bug until a better alternative can be found.... thanks Luke-Jr ;)
Mr. Bones says I had it right the first time, so reclosing bug. Users are expected to emerge -u world, using only an emerge -U world if they know what they are doing. A quick test showed that emerge -u world did fine for the bittornado upgrade.