LUN 866: Filter unpublished pages from CMS redirects 'add' view

I think you will need different cache keys for published/unpublished pages. Otherwise, if the first hit will be for published pages, those will get cached and they will get served from cache afterwards, even if filter_published is False. 

Also, since this will change too much from this part of the code, I think it's better to just use another field and widget in the cms-redirects module. Also, you might consider adding a page post_save hook and delete the redirect if the page gets unpublished.