wdb, second cut

Good progress on the worm database. Here's the second cut:
http://agilewiki.org/wiki/uuid/HdGvXx1XL6sRxDya4EUVYGGy

Seems pretty snappy too. I can do about 3,000 transactions/sec on my laptop with a slow disk (one insertion per tran).

Now that the basic logic is working, I also want to add a write cache to reduce multiple writes of the same block within the scope of a transaction.

I also need to add some threadlocking on get and prior. (Updates are single-threaded, so no problem with transactions.)