Updated GLSL uniform/sampler handling from gallium-0.1 branch

Previously, the shader linker combined the uniforms used by the vertex and
fragment shaders into a combined set of uniforms.  This made the implementation
of glUniform*() simple, but was rather inefficient otherwise.  Now each shader
gets its own set of uniforms (no more modelview matrix showing up in the
fragment shader uniforms, for example).

cherry-picked by hand from gallium-0.1 branch
diff --git a/src/mesa/shader/prog_instruction.h b/src/mesa/shader/prog_instruction.h
index aca7683..f8ff33e 100644
--- a/src/mesa/shader/prog_instruction.h
+++ b/src/mesa/shader/prog_instruction.h
@@ -413,12 +413,13 @@
     */
    GLint BranchTarget;
 
+#if 0
    /**
     * For TEX instructions in shaders, the sampler to use for the
     * texture lookup.
     */
    GLint Sampler;
-
+#endif
    const char *Comment;
 };