pages (blog/view): activate pagination when a single item is shown: `previous_page_url` and `next_page_url` are set when `item_id` is used. For now, they are both activated even if there is no item before or after, as it would request to make extra request to check it. This may be improved in 0.9 by using internal cache. fix 399

0.8.0b1.post1