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/LinearMath/btConvexHull.h

@@ -16,8 +16,8 @@ subject to the following restrictions:
 
 ///includes modifications/improvements by John Ratcliff, see BringOutYourDead below.
 
-#ifndef CD_HULL_H
-#define CD_HULL_H
+#ifndef BT_CD_HULL_H
+#define BT_CD_HULL_H
 
 #include "btVector3.h"
 #include "btAlignedObjectArray.h"
@@ -237,5 +237,5 @@ private:
 };
 
 
-#endif
+#endif //BT_CD_HULL_H