Thanks, that helped, but not directly. After reading your message, I 
remembered that I had, in fact, done a complete 'sup' before doing the 
snapshot overlay. In single-user mode, making userland and the kernel 
worked just fine, and the next reboot had me up to date.

I still think that we should have a clearly-documented method of going from 
1.4.1 to -current that works.