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/BulletCollision/CollisionShapes/btOptimizedBvh.h

@@ -15,8 +15,8 @@ subject to the following restrictions:
 
 ///Contains contributions from Disney Studio's
 
-#ifndef OPTIMIZED_BVH_H
-#define OPTIMIZED_BVH_H
+#ifndef BT_OPTIMIZED_BVH_H
+#define BT_OPTIMIZED_BVH_H
 
 #include "BulletCollision/BroadphaseCollision/btQuantizedBvh.h"
 
@@ -60,6 +60,6 @@ public:
 };
 
 
-#endif //OPTIMIZED_BVH_H
+#endif //BT_OPTIMIZED_BVH_H