add improved btGeneric6DofSpring2Constraint, thanks to Puhr Gabor and Tamas Umenhoffer!

improved the new demo testbed (work-in-progress)
add basic Lua demo, import URDF test, STL import, obj import

Demos3/AllBullet2Demos/GwenParameterInterface.h

@@ -12,6 +12,7 @@ struct GwenParameterInterface : public CommonParameterInterface
 	GwenParameterInterface(struct GwenInternalData* gwenInternalData);
 	virtual ~GwenParameterInterface();
 	virtual void registerSliderFloatParameter(SliderParams& params);
+    virtual void setSliderValue(int sliderIndex, double sliderValue);
 	virtual void syncParameters();
 	virtual void removeAllParameters();