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/bullet2/BasicDemo/Bullet2RigidBodyDemo.cpp

@@ -36,6 +36,11 @@ void Bullet2RigidBodyDemo::exitPhysics()
 	m_config=0;
 }
 
+void	Bullet2RigidBodyDemo::stepSimulation(float deltaTime)
+{
+	m_dynamicsWorld->stepSimulation(deltaTime);
+}
+
 Bullet2RigidBodyDemo::~Bullet2RigidBodyDemo()
 {
 	btAssert(m_config == 0);