AP_NavEKF : Bug fix for height drift due to timer wrap-around
AP_NavEKF : Changed default IMU bias process noise to use smallest value
AP_NavEKF : fixed bug in height limit range
AP_NavEKF : fixed bug in velocity rate of change filter

This bug meant the velocity rate of change used to scale the GPS measurement variances was noisy and too small
Rover: only use pivot steering in AUTO modes
Rover: fixed EKF usage for rover

added barometer object, and use shared home object from AHRS. This
gives basic EKF operation.
HAL_Linux: added missing Util.cpp
autotest: fly the cruise rudder circuit a bit faster
AP_GPS: added have_vertical_velocity() function 

for use by EKF
Rover: removed unused variables

thanks to Mike McCauley
Plane: remove unused variables

thanks to Mike McCauley
AP_NavEKF : Prevents aliasing triggering innovation consistency check failures
AP_AHRS: Change airspeed_estimate to const in children of AP_AHRS

Allows roll/pitch controllers to use DCM's airspeed estimate. Thanks to Kevin Hester for assistance in finding this.
AP_NavEKF: fixed replay with current copter logs
AP_GPS: added fix type to setHIL
AP_NavEKF: set fix type in GPS replay
Rover: pass fix type to gps->setHIL()
Copter: pass fix type to gps->setHIL()
Plane: pass fix type to gps->setHIL()
HAL_PX4: support uartE for 2nd GPS