[rotorcraft] refactor guidance_h_ref and fix route_ref if both argumens for atan2 are zero

not really sure what the max_ref values should be in the case where the route_ref angle can't be computed...
set to max on both axes for now...

see also issue #521
[guidance_h_ref] turn some defines into static const
Don't use failed reads. Add debugging.
[guidance_h_ref] split up and fix ref max accel/speed calculation
Merge pull request #522 from flixr/guidance_h_ref_fixes

[rotorcraft] refactor guidance_h_ref and fix route_ref
[stabilization] attitude quat: fix psi angle
Merge pull request #524 from benlaurie/fix

ARDrone2: Don't use failed reads. Add debugging.
[rotorcraft] by default always reset attitude stab on mode change again

To only reset (psi setpoint to current value, reset ref, reset integrators) the attitude stabilization
if the previous mode was not using it, define NO_ATTITUDE_RESET_ON_MODE_CHANGE
[rotorcraft] ups, fix wrong endif
[tools] calibrate.py: make automatic noise threshold an option
mag calibration
Two new ArDrones (Hann)
Merge branch 'master' of github.com:paparazzi/paparazzi into tudelft5.0