- fix library updates special cases: should note all potential library
packages as conflicts. Then save_old_libraries can split stuff off old
sets to keep libraries that are not in the new packages. There's only
one slightly tricky part, which concerns moving stuff that's not really
needed out of $set->{older}.
- in interactive mode, make it ask questions whenever the user could get
frustrated.
- finish pulling the pkg_add code into Add.pm/Update.pm.
- figure out when to continue after some errors, which should not stop a
full update, for instance... or ignore already installed packages (mostly
done).
- get an update path for libraries to be able to adjust dependencies correctly.