Issue 3735: misbehaving tag sets

I tried ```autosave: true``` on the ```belongs_to :tag_set``` association, no results. I tried ```autosave: true``` on the ```has_one :owned_tag_set association```, same lack of results.

So I just settled for explicitly saving the parent tag_set when we were updating things from the owned_tag_set side.

http://code.google.com/p/otwarchive/issues/detail?id=3735