[#4801] Avoid using h.url_for_static when adding a public folder

As at this point there isn't a Flask app context yet and we can't call
the url_for function. But if I understand the code correctly we just
want a link to the root of the site, taking into account stuff like root
path settings etc

ckan/plugins/toolkit.py

@@ -344,7 +344,8 @@ def _add_public_directory(cls, config, relative_path):
             relative_path,
             'extra_public_paths'
         )
-        add_public_path(path, h.url_for_static('/'))
+        url = h._local_url('/', locale='default')
+        add_public_path(path, url)
 
     @classmethod
     def _add_served_directory(cls, config, relative_path, config_var):