toolbar: Tighten restrictions on when it's usable

/tb/ links are sadly used by spammers as a URL shortener.
Since their primary benefit is giving users easy access to
voting and the comments, it can be changed to only be shown
to logged in users, and only if they've opted in to toolbar
links. Other visitors of /tb/ will get directed to the comments
for the link (providing easy access to the link itself, should
they desire to continue)

r2/r2/controllers/toolbar.py

@@ -95,13 +95,18 @@ class ToolbarController(RedditController):
 
     @validate(link = VLink('id'))
     def GET_tb(self, link):
+        '''/tb/$id36, show a given link with the toolbar
+        If the user doesn't have the toolbar enabled, redirect to comments
+        page.
+        
+        '''
         from r2.lib.media import thumbnail_url
-
-        "/tb/$id36, show a given link with the toolbar"
         if not link:
             return self.abort404()
         elif link.is_self:
             return self.redirect(link.url)
+        elif not (c.user_is_loggedin and c.user.pref_frame):
+            return self.redirect(link.make_permalink_slow(force_domain=True))
         
         # if the domain is shame-banned, bail out.
         if is_shamed_domain(link.url, request.ip)[0]: