Merge branch 'master' of github.com:PX4/Firmware into fw_autoland
Merge branch 'fw_autoland' of github.com:PX4/Firmware into fw_autoland
Merge pull request #475 from PX4/fw_autoland

Autolanding for fixed wing
l1: fix constrain of sine_eta1
Merge pull request #497 from thomasgubler/l1_sine_eta1

l1: fix constrain of sine_eta1
Merge branch 'master' into inav_alt_gps. Use GPS for altitude estimation.
change _update_height_demand for test
add missing copy of variable
px4io: fixed the io_reg_{set,get} errors

this fixes the PX4IO state machine to avoid the io errors we were
seeing. There are still some open questions with this code, but it now
seems to give zero errors, which is an improvement!
px4io: FMU half of px4io error fixes
lsm303d: try to reset the lsm303d if it goes bad in flight

this is based on earlier work by Julian Oes
Hotfix: Announcing important messages via audio
Cleanup of Doxygen tags
attitude_estimator_ekf: acceleration compensation based on GPS velocity
Only read 5 values, then return
Fixed min value check, works for fixed wing now
Fix to allow setting again zero disarmed PWM values after boot
Minor warning and no error in case of zero value for disarmed
Fixed pwm limit to apply the proper limits / scaling
Fixed commander and IO startup sequence, in-air restart is operational in this shape