It is disabled by default, see Demos/Gpu2dDemo/btGpuDemoDynamicsWorld.h for instructions how to enable it
Cleaned up Extras/CUDA folder and libbulletcuda project
It is called bt3DGridBroadphase and btCudaBroadphase is now derived from it rater than from btSimpleBroadphase
Test of bt3DGridBroadphase was added to CDTestFramework