Add setter for Acceleration on physics objects.

OpenSim/Region/Physics/ChOdePlugin/ODECharacter.cs

@@ -841,6 +841,7 @@ namespace OpenSim.Region.Physics.OdePlugin
         public override Vector3 Acceleration
         {
             get { return _acceleration; }
+            set { _acceleration = value; }
         }
 
         public void SetAcceleration(Vector3 accel)

OpenSim/Region/Physics/ChOdePlugin/ODEPrim.cs

@@ -673,6 +673,7 @@ namespace OpenSim.Region.Physics.OdePlugin
                 }
                 return _acceleration; 
             }
+            set { _acceleration = value; }
         }