mesa: Disable GL_NV_primitive_restart extension in core contexts.

mesa: Disable GL_NV_primitive_restart extension in core contexts.

The NV formulation of primitive restart is turned on/off with
glEnableClientState/glDisableClientState.  These two functions don't
exist in core contexts, which mean that GL_NV_primitive_restart is
essentially useless...even broken.

However, leaving it on causes oglconform's primitive-restart-nv tests to
run in OpenGL 3.1 contexts, which results in them all failing.  This
patch causes 29 subtests to go from "fail" to "not run".

NOTE: This is a candidate for stable branches.

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