remove get_navigable_children method, as it's not used any more
improve Site model so that all sites have a well-defined hostname, but may be designated 'default' to respond to all requests.
Remove the Sites framework. We've got a better one, and having them both just makes the django admin confusing
New URL-building mechanism, using a single query and correctly supporting multiple sites
add mechanism to output relative URLs to pages where appropriate (i.e. omitting the hostname where it's the same as the current site)