HAL_Linux: run IO processes when we do a stop_clock()

this has the effect of allowing logging to progress in Replay where we
are running at much more than realtime speeds
Replay: generate dataflash logs in Replay

this allows the calculated EKF flight path to be compared with
different parameters by using replay
Copter: remove OF_Loiter from FLTMODE param descriptions

Also remove OF_Loiter reference in comments
No functional change
Copter: remove OF_Loiter PIDs and tuning
OptFlow: remove ADNS3080 image grabber example
Copter: move update_optflow to sensors.pde

No functional change
Copter: optflow instantiation format change

No functional change
Copter: add OPTFLOW to default logging
Copter: optflow logging minor format change
Copter: send optflow health in extended status
Plane: send optflow health in extended status
GCS_MAVLink: add OPTICAL_FLOW to ap_message enum
Copter: send OPTICAL_FLOW msg to GCS
Plane: send OPTICAL_FLOW msg to GCS
Replay: prevent float exception in log writing
HAL_PX4: FRAM does not support fsync

the fsync just wastes time reopening /fs/mtd
AP_GPS: fixed vertical velocity in Replay

fixed NavEKF use of velocity velocity
GCS_MAVLink: removed obsolete headers
GCS_MAVLink: initial implementation of MAVLink routing object

will be used to auto-route packets over all available links
GCS_MAVLink: added routing object to GCS_MAVLink