- Always use a double-buffered visual if one is available.

- Always use a double-buffered visual if one is available.
- Ensure that all colormaps created use the double-buffered visual if
  it exists. This prevents problems where DRI GL implementations fail
  to work unless the colormap visual matches the window visual matches the
  glX visual.
- Get around similar visual issue with the default GL context created for
  apps that don't create their own contexts before trying to use GL functions.