add Bullet 2.x constraint solver tests for hinge, with large mass ratio

experiment with Midi controls in PairBenchmark to tune variables (will move it into a utility class, so every demo can easier use it in the future)
fix issue with broadphase, not initializing all pairs properly at pair array overflow

Demos3/AllBullet2Demos/main.cpp

@@ -40,7 +40,7 @@ void MyKeyboardCallback(int key, int state)
 			glPolygonMode( GL_FRONT_AND_BACK, GL_FILL );
 		}
 	}
-	if (key=='I' && state)
+	if (key=='i' && state)
 	{
 		pauseSimulation = !pauseSimulation;
 	}