Threader improvements

Threads are now sorted on demand when updated or rendered.  Not sure how
much of a performance hit this is going to be though...
New deferred Necromancy strategy for Robert

In a test of the new "Hollow Mind" AI engine, Robert will now watch
Scott's actions and, if a Vaccine is used to try to nullify Necromancy,
he will put off using it until the immunity has worn off.