Short Answer
At least for my case, it turns out you can force a restart and then repair packages.
Details
I followed @SauravKumar's advice in the comments and forced the system to restart. On reboot, the computer got to the purple screen where it selects which OS to run. If I chose the default Ubuntu, it started loading and then went to a black screen and didn't respond to the keyboard at all.
So I then booted in recovery mode and chose the check packages option. It found out that I was using a different version of etc/default/rcs
than the package maintainer. I chose to update it (the default is don't update) and then resumed booting and now it's running fine. Just to make sure, I rebooted again, and it works after a regular reboot too.
Update to 13.10: success!
Recovery Mode
? If yes then this link 2nd option would help you.. If not then I think you've to repair yourBoot-Entry
i,egrub-menu
through Boot-Repair give it a try..