Handling private and protected posts when querying multiple post types

[tamlyn]

When querying multiple post types (e.g. new WP_Query(array('slug'=>$slug, 'post_type'=>'any') the automatic handling of protected and private posts fails because it looks for capabilities 'edit_any' and 'read_any' which don't exist.

The attached patch illustrates the problem with a suggested fix. However it's possible I have misunderstood how this is supposed to work.

This is a known thing, really — It deliberately fails because it is not easy to construct sane SQL that will work individually across each post type + post_status pairing, as each post type is pretty much guaranteed to have different capabilities.

So essentially, you won't get back any private or protected posts unless you are querying a particular post type.

All ears on how to make this better.