OS X Yosemite 10.10.1 update - can't restart bug

I had this bug while trying to update to Yosemite 10.10.1 from Yosemite 10.8. It couldn't complete the update because it was stuck trying to restart. Finder would hang and the dock wouldn't leave. I couldn't even restart or shut down without hard powering it off by holding the power button down. sudo shutdown -r in a terminal didn't even work. The fix is to log in with safe mode. I loosely followed these odd directions, and the update applied normally in safe mode.