Aarrgh I found why it suddenly broke: I used
cvs -q update -APd .
and that introduced an incompatible change to the layout of the logical hostname structures!
So at least I know why it goes wrong now :-) So now I can just check if my corrections worked and then time-travel forward until I hit problems...
Pfff. How many times I've been stabbed in the back with those incompatible changes... I long to have cmucl stable and to start working on sbcl a bit more...