Add noindex, follow meta tag to intersection search queries

- ref: https://github.com/GigaOM/gigaom/issues/4538
- accompanying configuration update: https://github.com/GigaOM/gigaom/pull/4546
It's typically best to do the cheapest test first, since if it fails we won't spend time on more expensive tests.

In this case, we should probably test `TRUE == scriblio()->options['noindex_intersection_pages']` before doing the `array_sum()`. While at it, we should also probably break this into multiple lines.