Started off as minor changes, but then also updated how things work in core
logic. We've been making broken over-sized update CDs for a while, as the
code didn't check for being over-full properly. Used to work better when we
had smaller packages, but now it's not working. Change to the method used in
the main debian-cd code: add packages one at a time until we go over, then
remove the last package. Works fine now.