AP_AHRS: make airspeed_estimate const
AP_GPS: make last_message_time_ms const
AP_Math: allow vector3 and matrix3 objects to be used as arrays
GCS_MAVLink: removed unused variable
Rover: added RC in/out logging
AP_AHRS: changed default GPS lag to 1 sample

this is based on detailed logs from a LEA-6H and NEO-7N
Rover: split up GPS update into 10Hz and 50Hz parts
Rover: prepare for 2.44 release