Add multiple post type support to update_object_term_cache()

[johnbillion]

update_object_term_cache() only accepts one post_type. If a loop contains more than one post type then the object term cache isn't populated and your queries can go through the roof.

See ​http://lists.automattic.com/pipermail/wp-hackers/2010-September/034776.html

Patch coming up.

[johnbillion]

Patch.

This patch changes update_post_caches() so it calls update_object_term_cache() for each post type in the $posts array if the $post_type parameter isn't set or it's set to 'any'.

[nacin]

We should probably adjust update_object_term_cache() to accept multiple post types instead, that way we still keep to a single wp_get_object_terms() call.

Support for it should probably be pretty easy. Simply call get_object_taxonomies() for each post type and merge the result, I think.

[johnbillion]

That does indeed work.

Updated patch changes update_object_term_cache() so it accepts a single object type or an array of object types.

update_post_caches() is also modified so it passes an array of the post types from the $posts array if $post_type is set to 'all'.

[nacin]

Turns out get_object_taxonomies() can handle an array. I honestly hadn't checked originally, sorry about that. Closing as a duplicate of #15026, now fixed.