Office/rolling chairs will now work properly when carrying mobs, those will not slip out of the chair, becoming an ungrabless mobs. And the direction of the chair and mob will be better and easier to notice when they bump something.

Their direction changes will work even better if mob movement code finally removes all the spawn() calls. I'm not planning of adding any special code for that here.
Merge pull request #4057 from Aranclanos/OfficeChairs

Rolling chairs fixes.