[Pharo-project] I'm going to integrate Metacello into Pharo 2.0

Hi, Just as Gofer, it is just too important to keep it outside. Also, most of our packages now are loaded through a configuration (if there is one god, thanks him for that :), so it will be in most installations anyway. Of course, I will make sure that it is unloaded in a #cleanUpForProduction. Cheers, Esteban