Take the hungry boarfiend to Nightshadow Bogg and kill mushrooms until the boarfiend explodes If your boarfiend vanishes without updating, return to Madam Victra for a new boarfiend. (I recomment restarting the quest before getting a new boarfiend, as I was not able to get the update without restarting even after getting a new one.)
The quest will also only update if you are in the correct area (as shown by the RoI on the map).
If you are having trouble getting the update, try killing the shrooms one at a time. Killing them two or three at a time or being in combat when the boar explodes seems to mess up the quest, and you'll have to restart.
7/8/2012 ** After having tried everything I've read online about how to get this update, I gave up on these tricks and received the update while killing swiftly (with a merc), while in combat, and after having gotten a new boar multiple times without deleting and restarting the quest. Just get a new boar and keep trying until you get the update.
5/21/2015: quest works! You MUST KILL 10 mushroom guys to get the update. Ensure you are in the correct area and single pull them to be sure. Be persistent - there is no try.