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/btConvexPenetrationDepthSolver.h

@@ -14,8 +14,8 @@ subject to the following restrictions:
 */
 
 
-#ifndef __CONVEX_PENETRATION_DEPTH_H
-#define __CONVEX_PENETRATION_DEPTH_H
+#ifndef BT_CONVEX_PENETRATION_DEPTH_H
+#define BT_CONVEX_PENETRATION_DEPTH_H
 
 class btStackAlloc;
 class btVector3;
@@ -38,5 +38,5 @@ public:
 
 
 };
-#endif //CONVEX_PENETRATION_DEPTH_H
+#endif //BT_CONVEX_PENETRATION_DEPTH_H