Copter: Leonard's fix for trapezoidal frame

We need to allow yaw_factors to be floats in the add_motor method
AP_HAL: define RC_12

we have 12 channels on PX4FMU+PX4IO
HAL_PX4: support 12 output channels with PX4IO

first 8 on IO board, next 4 on FMU outputs
HAL_PX4: setup for 12 output channels

moved telemetry port to /dev/ttyS2 to free PWM outputs on FMU
RC_Channel: support 8 auxillary RC channels

needed for full 12 channel support on PX4
Copter: support all 12 channels on PX4

last 4 channels are on the FMU pins
Plane: if airspeed enabled, require 5m/s to unsuppress throttle
Plane: support 12 output channels on PX4
Copter: add I2C error count to PM message
Plane: add I2C error count to PM message
Rover: add I2C error count to PM message
AutoTest: reduce copter turn rate in fly square
AC_Fence: first implemenation of library
Copter: integrate AC_Fence in place of limits

Lesser functionality than limits but saves more than 150 bytes and it
works
Copter: correct fence parameter
Copter: adopt compass test from arduplane
AutoTest: add valgrind test script for randy
Copter: pre-arm check for compass
Rover: show modes as strings in log
Plane: show modes as strings in log