Consensus testing

Decided that this is a good stopping place.

I added a good amount of testing to the consensus package, but I'm probably only about 40% of the way to completion. I made more changes to the actual consensus code than I was expecting, but they should all be non-forking.

maintenance.go needs a little more work, verifytransaction.go needs a lot more work, and then I need to write a bunch of tests that use full blocks.

After that the persist stuff needs to be changed and updates need to be written for that.

Then the notifications.

Finally, there are some logic changes to the synchronize package that will eventually be necessary for DoS purposes (you don't accept blocks that don't extend the longest chain unless you first get a set of headers that demonstrate a longer chain).