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/GpuDemos/rigidbody/GpuRigidBodyDemo.h

@@ -8,6 +8,7 @@ class GpuRigidBodyDemo : public GpuDemo
 {
 protected:
 	class GLInstancingRenderer* m_instancingRenderer;
+	class GLPrimitiveRenderer*	m_primRenderer;
 	class b3gWindowInterface*	m_window;
 
 	struct GpuRigidBodyDemoInternalData*	m_data;