Fix JSBsim trimming on reposition.

- remove the entire /fdm tree on reposition
- force the initial NED wind values to 0.0 in JSBsim,
pending advice from people who know better.

src/FDM/JSBSim/JSBSim.cxx

@@ -389,9 +389,7 @@ void FGJSBsim::init()
       Winds->SetProbabilityOfExceedence(0.0);
     }
 
-    fgic->SetWindNEDFpsIC( -wind_from_north->getDoubleValue(),
-                           -wind_from_east->getDoubleValue(),
-                           -wind_from_down->getDoubleValue() );
+    fgic->SetWindNEDFpsIC(0.0, 0.0, 0.0);
 
     SG_LOG(SG_FLIGHT,SG_INFO,"T,p,rho: " << Atmosphere->GetTemperature()
      << ", " << Atmosphere->GetPressure()

src/Main/fg_init.cxx

@@ -952,6 +952,8 @@ void fgStartReposition()
   fgSetBool("/sim/crashed", false);
   
   globals->get_subsystem("flight")->unbind();
+    
+  globals->get_props()->removeChild("fdm");
   
   // update our position based on current presets
   // this will mark position as needed finalized which we'll do in the