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/btPolyhedralContactClipping.h

@@ -17,8 +17,8 @@ subject to the following restrictions:
 ///This file was written by Erwin Coumans
 
 
-#ifndef __POLYHEDRAL_CONTACT_CLIPPING_H
-#define __POLYHEDRAL_CONTACT_CLIPPING_H
+#ifndef BT_POLYHEDRAL_CONTACT_CLIPPING_H
+#define BT_POLYHEDRAL_CONTACT_CLIPPING_H
 
 
 #include "LinearMath/btAlignedObjectArray.h"
@@ -42,5 +42,5 @@ struct btPolyhedralContactClipping
 
 };
 
-#endif // __POLYHEDRAL_CONTACT_CLIPPING_H
+#endif // BT_POLYHEDRAL_CONTACT_CLIPPING_H