add the BT_ prefix for all #ifdef guards, to avoid conflicts with developers own header defines.

Fixes Issue 497

//license header
#ifndef BT_RIGIDBODY_H
#define BT_RIGIDBODY_H
class btRigidBody
{
};
#endif //BT_RIGIDBODY_H

src/BulletDynamics/Vehicle/btRaycastVehicle.h

@@ -8,8 +8,8 @@
  * of this software for any purpose.  
  * It is provided "as is" without express or implied warranty.
 */
-#ifndef RAYCASTVEHICLE_H
-#define RAYCASTVEHICLE_H
+#ifndef BT_RAYCASTVEHICLE_H
+#define BT_RAYCASTVEHICLE_H
 
 #include "BulletDynamics/Dynamics/btRigidBody.h"
 #include "BulletDynamics/ConstraintSolver/btTypedConstraint.h"
@@ -232,5 +232,5 @@ public:
 };
 
 
-#endif //RAYCASTVEHICLE_H
+#endif //BT_RAYCASTVEHICLE_H