NV_path_rendering support

I've implemented support for tracing NV_path_rendering API usage.

You can try out this support on the NV_path_rendering SDK (NVprSDK) examples.  See:

  http://developer.download.nvidia.com/assets/gamedev/files/NVprSDK.zip
  http://developer.download.nvidia.com/assets/gamedev/files/NVprDEMOs.zip
  https://developer.nvidia.com/gpu-accelerated-path-rendering

Changes are to:

helpers/glsize.hpp
specs/glapi.py
specs/glparams.py

I also improved the EXT_direct_state_access completeness for what Cg Toolkit 3.1 uses.

- Mark Kilgard, NVIDIA