Comment 3 for bug 431993

The purpose of cleaning up directories that might be owned by the system is that if we do not do this then we have no chance whatsoever of being able to support the resulting conjoined-twin system. We need to clear out anything put there by the previous *operating system*, while preserving *user data*. It's a delicate balancing act and tends to involve a lot of special cases; when we miss a case we get bugs like these.