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/btWheelInfo.h

@@ -8,8 +8,8 @@
  * of this software for any purpose.  
  * It is provided "as is" without express or implied warranty.
 */
-#ifndef WHEEL_INFO_H
-#define WHEEL_INFO_H
+#ifndef BT_WHEEL_INFO_H
+#define BT_WHEEL_INFO_H
 
 #include "LinearMath/btVector3.h"
 #include "LinearMath/btTransform.h"
@@ -115,5 +115,5 @@ struct btWheelInfo
 
 };
 
-#endif //WHEEL_INFO_H
+#endif //BT_WHEEL_INFO_H