When a peer offers us a sync block from a fork that is too old for us to switch to (>400 blocks ago), inhibit fetching any further blocks from them, but allow them to remain connected to us so they can fetch the rest of our blocks and hopefully switch to our fork.  Once they receive all of our blocks, disconnect from them.  Our previous behavior was to disconnect as soon as they sent us the first block from the old fork, and that made it impossible for them to ever catch up to the one true fork.
Add a range of p2p protocol message codes that are ignored for future expansion.
Clean up a few compiler warnings.