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/btEmptyShape.h

@@ -13,8 +13,8 @@ subject to the following restrictions:
 3. This notice may not be removed or altered from any source distribution.
 */
 
-#ifndef EMPTY_SHAPE_H
-#define EMPTY_SHAPE_H
+#ifndef BT_EMPTY_SHAPE_H
+#define BT_EMPTY_SHAPE_H
 
 #include "btConcaveShape.h"
 
@@ -67,4 +67,4 @@ protected:
 
 
 
-#endif //EMPTY_SHAPE_H
+#endif //BT_EMPTY_SHAPE_H