Fix for chained iterators when a single instance is requested.
Merge branch 'single_iter_fix' into iji_2
Merge pull request #803 from sorlok/single_iter_fix

Change `fetch_inst_iter_by_id`; return iterator to only one instance.
The instance_deactivated list is never cleared between rooms.
Merge branch 'clear_deact' into iji_2