Log a message with the height when we get duplicate blocks.
Downgrade some verifier errors and warnings to info and debug, because
some peers on mainnet consistently provide bad blocks.
Reduce the amount of time that the block verifier waits for the previous
block, before polling again.
(Waiting for 2 seconds resulted in some apparent block verifier hangs.)
This is a temporary fix, until the state layer handles context checks.
* Flatten consensus::verify::* to consensus::*
* Move consensus::*::tests into their own files
* Move CheckpointList into its own file
* Move Progress and Target into a types module
QueuedBlock and QueuedBlockList can stay in checkpoint.rs, because
they are tightly coupled to CheckpointVerifier.
teor