Allow admins to edit topics by the "generic user"

This will allow admins to edit topics posted automatically by the
scheduling system.

tildes/tildes/models/topic/topic.py

@@ -307,10 +307,15 @@ class Topic(DatabaseModel):
         acl.append((Allow, Authenticated, "comment"))
 
         # edit:
-        #  - only text topics can be edited, only by the author
+        #  - only text topics can be edited
+        #  - authors can edit their own topics
+        #  - admins can edit topics belonging to the generic/automatic user
         if self.is_text_type:
             acl.append((Allow, self.user_id, "edit"))
 
+            if self.user_id == -1:
+                acl.append((Allow, "admin", "edit"))
+
         # delete:
         #  - only the author can delete
         acl.append((Allow, self.user_id, "delete"))