registration has trouble if dateobs and registered disagree

[watersc1]

registration became backed up on 2011-04-09 because dateobs fell before the registration cutoff and "registered" fell after. This meant that half the system was waiting for the exposure to be burntooled, and the other half considered it unnecessary to burntool. This is apparently a very rare condition, but still needs to be fixed. Given that we now have the --continue option, perhaps it's worthwhile to let everything from UTC midnight onward be burntooled.