commander: Enforce (in presence of power sensing) that a) system is not purely servo rail powered and b) power rail voltage is higher than 4.5V on the main avionics rail
systemlib: Add circuit breakers
commander: put circuit breaker into effect
system status topic: Add support for circuit breaker
mc_att_control: Support circuit breakers
px4io driver: Add support for circuit breakers
Merge branch 'master' into power_enforce
Merged master into power_enforce
Merge branch 'master' of github.com:PX4/Firmware into power_enforce
Merge branch 'master' of github.com:PX4/Firmware into power_enforce
commander: Minor checks / improvements to power enforce patch
Merge pull request #1005 from PX4/power_enforce

Disallow servorail-only powered flight.