This patch reworks busyobj handling so that busyobjs are owned by the issuing worker, and the worker should explicitly release it when done with it. A busy objcore only lends a pointer to it. This is to fix the current situation where the owning party is murky, and the current code will leak busyobjs in at least one situation.

BusyObj's are reference counted in preperation for the streaming code.

Patch also adds several asserts to help make sure the busyobjs are sound.

Fixes: #1068