Reboot during startup with recent head

Hi,

I rebuilt head (r242605) in a VMware virtual machine a couple of days ago, and
now it won't boot anymore. The loader menu appears, the countdown starts, and boom,
reboot. I tried a fresh head (r242700) but the problem remains.

Going back to r242205 solves the problem, so this was introduced somewhere
between r242205 and r242605.

I managed to record the entire thing with my phone before I had to leave for
work today. You can see it here:

  http://mirror.vnode.se/upload/head-reboots.mov

Any ideas? Any specific revision I should try to back out?

-- 
Joel