update counters for forum when topic was deleted directly (for example from admin interface)
select related user model in get_last_post

full select_related in get_last_post in Topic model may cause slow queries when used
moved all permission-related checks to permission handler
added unittest for custom permission handler
remove unused functions
don't allow subscribing to topics which one is not allowed to see (potential information leak)
Merge branch 'master' into pluggable_authorization