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/btContactConstraint.h

@@ -13,8 +13,8 @@ subject to the following restrictions:
 3. This notice may not be removed or altered from any source distribution.
 */
 
-#ifndef CONTACT_CONSTRAINT_H
-#define CONTACT_CONSTRAINT_H
+#ifndef BT_CONTACT_CONSTRAINT_H
+#define BT_CONTACT_CONSTRAINT_H
 
 #include "LinearMath/btVector3.h"
 #include "btJacobianEntry.h"
@@ -65,4 +65,4 @@ void resolveSingleBilateral(btRigidBody& body1, const btVector3& pos1,
 
 
 
-#endif //CONTACT_CONSTRAINT_H
+#endif //BT_CONTACT_CONSTRAINT_H