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/BulletDynamics/ConstraintSolver/btSliderConstraint.h

@@ -22,8 +22,8 @@ TODO:
  - add conversion for ODE constraint solver
 */
 
-#ifndef SLIDER_CONSTRAINT_H
-#define SLIDER_CONSTRAINT_H
+#ifndef BT_SLIDER_CONSTRAINT_H
+#define BT_SLIDER_CONSTRAINT_H
 
 
 
@@ -329,5 +329,5 @@ SIMD_FORCE_INLINE	const char*	btSliderConstraint::serialize(void* dataBuffer, bt
 
 
 
-#endif //SLIDER_CONSTRAINT_H
+#endif //BT_SLIDER_CONSTRAINT_H