HAL_Empty: avoid some float conversion warnings
HAL_PX4: avoid some float conversion warnings
build: disable some compiler errors for now

this needs more work, but allows us to build with upstream PX4
Firmware now
Copter: Don't use land detector to stop stabilizing in stabilize
Arducopter: Improve comments for scheduler.  Add timing table for AVR processors.
TradHeli: Create new function to move data between AP_MotorsHeli and AP_AttitudeControl.
TradHeli: Add Mode Filter on RC8 input for RSC Controller.
TradHeli: Cause DDVP Tail Motor to stop immediately when Ch8 is 0.
AC_HELI_PID: Add feedforward accessor functions.
Arducopter: Add independent rate roll and pitch P, I, D tuning options.  Add rate feedforward tuning options for tradheli.
TradHeli: Add Heli.h file
AC_AttControl_Heli: Add LPF filter to Rate Feedforward terms
TradHeli: Initialize Rate FF filters.
AP_MotorsHeli: Add main loop rate time variable and method.  Change RSC increment calc to account for loop rate time.
TradHeli: Set main loop rate time in motors class.
TradHeli: Acro mode uses full collective range.
TradHeli: Stabilize mode should use get_pilot_desired_collective, not get_pilot_desired_throttle.
TradHeli: Change behavior of Acro and Stabilize modes when disarmed.  Servos should move realistically for testing when disarmed.
AP_MotorsHeli: Create Delta Phase Angle variable and method to set.  Will be used by CCComp code.
AP_MotorsHeli: Change set_delta_phase_angle so that it forces recalculation of collective factors.