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/NarrowPhaseCollision/btConvexCast.h

@@ -14,8 +14,8 @@ subject to the following restrictions:
 */
 
 
-#ifndef CONVEX_CAST_H
-#define CONVEX_CAST_H
+#ifndef BT_CONVEX_CAST_H
+#define BT_CONVEX_CAST_H
 
 #include "LinearMath/btTransform.h"
 #include "LinearMath/btVector3.h"
@@ -70,4 +70,4 @@ public:
 					CastResult& result) = 0;
 };
 
-#endif //CONVEX_CAST_H
+#endif //BT_CONVEX_CAST_H