Help with crashdump

[walt]

After this morning's cvsup I got a kernel panic during boot.  The last
panic I got was at least a year ago, so I can't remember the details
of what to do.

At the debugger prompt I typed 'panic' and watched the dump happen,
so I know it actually did dump something -- to somewhere.

I expected something to happen when I rebooted with the old kernel,
but there was no message about finding a crashdump, and nothing in
/var/crash.  I did get a message about / not being properly
dismounted and a successful fsck, but that's all.

I have dumpdev="/dev/ad1s5b" in /etc/rc.conf and that really is my
swap partition.

I must be forgetting something important -- but what?