FP64 Support Revised For R600g Gallium3D Driver

While the Radeon HD 5000/6000 series were advertised as supporting up to OpenGL 4.4 and are supported that way by the Catalyst / Radeon Software proprietary driver, the Mesa R600g driver has only exposed OpenGL 3.3 (with the exception of the HD 5800 / 6900 series) due to lacking FP64 support. That emulated FP64 support is now stepping ahead for the R600g driver...