The issuses section of GL_NV_fog_distance says:

    How does this extension interact with the EXT_fog_coord extension?

         If FOG_COORDINATE_SOURCE_EXT is set to FOG_COORDINATE_EXT, then
         the fog distance mode is ignored.  However, the fog distance
         mode is used when the FOG_COORDINATE_SOURCE_EXT is set to
         FRAGMENT_DEPTH_EXT.  Essentially, when the EXT_fog_coord
         functionality is enabled, the fog distance is supplied by the
         user-supplied fog-coordinate so no automatic fog distance
         computation is performed.

A heavily modified version of this test passes on a Geforce3 (NV20)
running NVIDIA's 71.86.15 drivers.  These are the last drivers that
support NV10 through NV2x, and they are shipped in 2011.

v2: Use piglit_draw_rect_z and fix a space-before-tab problem.  Both
suggested by Eric.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>