registry2.0 ready for debugging

[Joshua Root]

I've hooked up registry2.0 sufficiently to allow ports to be installed,
so now is the time for brave souls to start trying it out. With a trunk
build, you just need to set 'portdbformat sqlite' in macports.conf.

The main issue at the moment is that the registry's entry "objects"
(actually commands like "registry::entry0") are not in scope sometimes,
which prevents port {uninstall,deactivate,activate} from working. If you
figure out this or any other problem, please feel free to commit a fix. :-)

- Josh