add additional callback

src/BulletCollision/NarrowPhaseCollision/btPersistentManifold.cpp

@@ -21,6 +21,8 @@ subject to the following restrictions:
 btScalar					gContactBreakingThreshold = btScalar(0.02);
 ContactDestroyedCallback	gContactDestroyedCallback = 0;
 ContactProcessedCallback	gContactProcessedCallback = 0;
+ContactStartedCallback		gContactStartedCallback = 0;
+ContactEndedCallback		gContactEndedCallback = 0;
 ///gContactCalcArea3Points will approximate the convex hull area using 3 points
 ///when setting it to false, it will use 4 points to compute the area: it is more accurate but slower
 bool						gContactCalcArea3Points = true;