branch mw4: add missing header
branch mw4: add Xplane plugin with SCALEACCEL=1.29
branch mw4: SILsim/Xplane9 IMU working better
branch mw4: rmat.c bugfix, KP/KIrollpitch adjusted for SILsim/Xplane9
branch mw4: rmat.c bugfix, test slip/skid control in SILsim/Xplane9