i965: Do lowering of array indexing of a vector in the FS.

Fixes a regression in ember since switching to the native FS backend,
and the new piglit tests glsl-fs-vec4-indexing-{2,3} for catching this.

src/mesa/drivers/dri/i965/brw_fs.cpp

@@ -118,6 +118,7 @@ brw_link_shader(struct gl_context *ctx, struct gl_shader_program *prog)
 	 lower_if_to_cond_assign(shader->ir, 16);
 
       do_lower_texture_projection(shader->ir);
+      do_vec_index_to_cond_assign(shader->ir);
       brw_do_cubemap_normalize(shader->ir);
 
       do {