Don't disable low-battery hibernate

[szhu]

If NoSleep is turned on for a laptop, it will drain its battery without sleeping, preventing the state from being restored when the machine is turned on again.

Proposal: turn NoSleep off when the battery is dangerously low (possibly by listening for a power notification — kIOPMPowerEmergency?). Ideally this should be an option and should be on by default.

[ricburton]

+1. Would be great to have this feature.

[vprasanth]

+1