deep copies

Release 8.1 has been posted, the transactional API has been revised, the new threading model has been put in place and tests have been devised for exercising the new threading model. Time to move on to the next item.

I've been thinking a lot about deep copies, which should be very quick on a COW database. It should only be a matter of refactoring some of the existing code which handles the forking of a branch.

Deep copies are something you want to be able to do in any case in an object store, only the Copy-On-Write technology should make it very efficient. And it seems like a very important feature--how else can you implement undo/redo?