Add check that texture manager destroys old textures
Add check that texture manager destroys old textures

likangning93/cesium,likangning93/cesium,likangning93/cesium,CesiumGS/cesium,likangning93/cesium,AnalyticalGraphicsInc/cesium,AnalyticalGraphicsInc/cesium,likangning93/cesium,CesiumGS/cesium,CesiumGS/cesium,CesiumGS/cesium,CesiumGS/cesium