FMUv1: setup SPI pins as 50MHz on PX4v1
FMUv2: fixed UART3 flow control pins
px4io: support PX4IO_P_SETUP_FORCE_SAFETY_OFF 

this allows the FMU to force the safety off on the IO board. Useful in
two cases:

 1) vehicles where the safety switch is impractical or not useful
 (eg. HAB planes or internal combustion motors)

 2) doing ESC calibration on multi-copters
pwm: added PWM_SERVO_SET_FORCE_SAFETY_OFF ioctl

this allows the safety switch on px4io to be forced off
uORB: added an ORB topic for system_power

holds power supply state and 5V rail voltage on FMUv2
adc: publish system_power ORB topic from ADC
meas_airspeed: correct MS4525 airspeed using 5V rail voltage

the slope seems to be reasonably consistent between sensors
meas_airspeed: added temperature compensation with voltage too
airspeed: cope properly with reversed tubes on pitot tube

report both a raw (signed) and non-raw (unsigned) differential
pressure. The signed value needs to be used for calibration to prevent
a bias at low airpeeds if the tubes are reversed
MPU6000: gyro topic was not initialized
tests: added "tests file2" filesystem test

this is useful for testing for filesystem corruption on cluster
boundaries
FMUv2: switch debug console and 2nd GPS

this allows a normal GPS cable to be used for the 2nd GPS, making
dual-GPS setups easier
hmc5883: properly reset mag to normal state on calibration fail

and add current output in "hmc5883 info"
Merge remote-tracking branch 'upstream/master'