Re-implement GLSL texture sampler variables.

GLSL sampler variables indicate which texture unit to use for TEX instructions.
Previously, this was baked into the fragment/vertex program and couldn't be
readily changed once set.
Now, SamplerUnits[] array indicates which texture unit is to be used for
each sampler variable.  These values are set with glUniform1i().
This is extra state that must be passed to the fragment/vertex program
executor at runtime.

src/mesa/pipe/softpipe/sp_state_sampler.c

@@ -78,3 +78,17 @@ softpipe_set_texture_state(struct pipe_context *pipe,
 
    softpipe->dirty |= SP_NEW_TEXTURE;
 }
+
+
+void
+softpipe_set_sampler_units(struct pipe_context *pipe,
+                           uint num_samplers, const uint *units )
+{
+   struct softpipe_context *softpipe = softpipe_context(pipe);
+   uint i;
+   for (i = 0; i < num_samplers; i++)
+      softpipe->sampler_units[i] = units[i];
+   softpipe->dirty |= SP_NEW_SAMPLER;
+}
+
+