Fix YASim's /accelerations/pilot/{x,y,z}-accel-fps_sec computations. These

Fix YASim's /accelerations/pilot/{x,y,z}-accel-fps_sec computations.  These
are the accelerations (forces) as felt from the pilot's perspective.  This
combines the accelerations due to change in velocity vector and gravity.

Previosly the gravity part was right, but the body accelerations were being
transformed incorrectly.  The error was very subtle and basically amounted to
the fact that inverting an axis of a vector before transforming it is not
equivalent to transforming the vector and then inverting that axis.

After this fix, pilot accelerations + gyro + gps can be fed into an external
kalman filter and it will converge properly (extra confirmation that there
was a problem and this fix corrects it.)