- Only prototype the interfaces which are subclassed (I overdid it
  last time!).
- Implement Get/Set Texture and GetBackBuffer, plus device's
  GetDisplayMode / GetDeviceCaps.
- Make some of the d3d9 skeleton code issue fixme's to highlight code
  which hasn't been migrated yet.
- Correct the d3d9 headers for D3DSURFACE_DESC which caused stack
  corruption in demos.