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/BulletMultiThreaded/TrbStateVec.h

@@ -14,8 +14,8 @@ subject to the following restrictions:
 
 */
 
-#ifndef __TRBSTATEVEC_H__
-#define __TRBSTATEVEC_H__
+#ifndef BT_TRBSTATEVEC_H__
+#define BT_TRBSTATEVEC_H__
 
 #include <stdlib.h>
 #ifdef PFX_USE_FREE_VECTORMATH
@@ -334,5 +334,6 @@ void TrbState::reset()
 	angularDamping = 0.99f;
 }
 
-#endif /* __TRBSTATEVEC_H__ */
+#endif //BT_TRBSTATEVEC_H__
+