Apple - Force macbook to sleep when lid closed and external monitor connected in Lion

This worked in 10.7 and 10.8 with my MacBook Air:

sudo nvram boot-args=iog=0x0

After restarting, it should restore the pre-10.7 behavior:

• Closing the lid puts a laptop to sleep even when it is connected to an external display
• If you then wake the laptop up and open the lid, the internal display doesn't turn on

To undo it, run sudo nvram -d boot-args or hold ⌥⌘PR on startup.