Process previous/next post navigation with category exclusions

[coppit]

There should be a call to the list_cats_exclusions filter from within get_next_post and get_previous_post, similar to the way it's already done in list_cats.

This way plugin authors can hook list_cats_exclusions and modify the accessible posts in both the category list and the navigational post links.

For example, my Category Access plugin hides posts in particular categories. Without the requested hook, my plugin can't avoid the next post pointing to a post that should be hidden from the user.

[matt]

Fixed this earlier.

[stewartjohnson]

This isn't actually fixed, see the bug I just opened: #4304