* Use spandoc correctly
* Refactor consensus test error handling
* Delete a checkpoint test that will soon be obsolete
* Only initialise tracing once for the block tests
* Use tracing in the checkpoint tests
* Move BlockVerifier and tests into block.rs
* Update a BlockVerifier comment
* Tweak some TODO comments
node_time_check() is a small function, so we inline it into its callers.
(And then rename node_time_check_helper() to node_time_check().)
Part of #477.
teor