Broadcasting and Bootstrapping

The former is pretty much done. The latter needs work. Here's how bitcoin does it (more detail). We will probably use their inventory/header system:

1. Ask a node to get you up to speed
2. Compare blocks with the node until you find one you both have
3. Receive headers for all blocks between that block and the current block
4. Download actual block data Right now the bootstrapping code asks for blocks at a specific height, instead of with a specific hash. I imagine there's a reason Bitcoin does it the other way; maybe you have some thoughts?