Added an extra path to check for linux power supply status.
Added ignore battery option. If set to true, then when we can't figure out
the power status, we'll assume the system is plugged in.
source, and CPU has been idle for some time, then begin mining to some
threshold (don't destroy the users' CPU).
This patch only supports windows and linux (I've only tested on Win64 and
Ubuntu).
The variables currently default to pretty conservative values (i.e. 20%
CPU mining threshold).