- figure out when to continue after some errors, which should not stop a
full update, for instance... or ignore already installed packages (mostly
done).
-- make sure all user-interface is done through a few functions, so that it's
-easy to plug another interface in (mostly done)
-- don't close Location unconditionally while looking for updates. In most
-cases, we're going to install this package right away, so we should try to
-keep it open to avoid spurious ftp disconnects.
- get an update path for libraries to be able to adjust dependencies correctly.