- 'orderby' => 'include' requires an array of post_ids via the include collection param.
- 'orderby' => 'id' and 'orderby' => 'slug' need map the correct WP_Query equivalents.
Merges [39440] to the 4.7 branch.
Props flixos90, hnle, dd32, rachelbaker, joehoyle, pento.
Fixes#38971 for 4.7.
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