[PATCH] dri2: Fix authentication for < v8 clients.

[Knut Petersen]

xserver master, glxgears with normal user privileges:
i915 and swrast fail to load. Nevertheless: glxgears runs, tells
that DRI is unavailable and something about 60 FPS. In reality
only a few frames are really drawn every second.

xserver master, glxgears with root privileges:
glxgears runs smoothly with about 170 FPS
but without hardware acceleration.

3f97284b10c250457888902debd4d793cb4544d4 reverted:
Everything is fine.

Either revert 3f9728 (probably not a good idea) or fix the legacy authentication problem.

cu,
  Knut