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
AP_HAL: support uartE
HAL_AVR: no uartE
HAL_Empty: no uartE
HAL_FLYMAPLE: no uartE
HAL_SITL: support a 2nd GPS
DataFlash: added GPS2 logging
Plane: support a 2nd GPS
Rover: support a 2nd GPS