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/btSolve2LinearConstraint.h

@@ -13,8 +13,8 @@ subject to the following restrictions:
 3. This notice may not be removed or altered from any source distribution.
 */
 
-#ifndef SOLVE_2LINEAR_CONSTRAINT_H
-#define SOLVE_2LINEAR_CONSTRAINT_H
+#ifndef BT_SOLVE_2LINEAR_CONSTRAINT_H
+#define BT_SOLVE_2LINEAR_CONSTRAINT_H
 
 #include "LinearMath/btMatrix3x3.h"
 #include "LinearMath/btVector3.h"
@@ -104,4 +104,4 @@ public:
 
 };
 
-#endif //SOLVE_2LINEAR_CONSTRAINT_H
+#endif //BT_SOLVE_2LINEAR_CONSTRAINT_H