[Xorg] DRI merging

[Alan Cox]

> Where DRI is not supported it's not used, why should any other driver be
> forced to work every where?

All the current drivers barring some OS specific things like Linux frame
buffer driver work when DRI isnt available on that platform and fall
gracefully back to 2D with software 3D, including those that when DRI is
available use the DRI layer for 2D.

This is an important part of the XFree/Xorg tradition.