Update from JSBSim

Update from JSBSim

Changed _set_Accels_Pilot_Body to use FGAuxiliary::GetNpilot instead
of FGAuxiliary::GetPilotAccel.  It looks like a similar change was
started but never finished, and there are artifacts still lingering.
With this change, the slip/skid ball now works reasonably on the C172
when in motion, but not at rest (that will have to wait for fixes to
the gear code).