Add extra debugging messages for download and stall logic.
Stripe downloads (so not a contiguous chunk is requested from one node).
Disable sipa stall disconnect logic, but still log when it would have been triggered.
Disconnect no longer useful peers.
Find the runt of the litter (and disconnect it).
Reset variables when network changed.
Allow many blocks to be received in one go from a peer for up to 1 second.

This speeds up IDB.
Detect when headers downloading is stalling.