GA release v1.0.28

Many additions since 1.0.21. The ultimate breakdown is v1.0.21...v1.0.28

Notable:

• support for DATETIME subsecond resolution
• user-commanded throttling implies complete silence, not even heartbeat is written
• fixed log_slave_updates check on --test-on-replica and --migrate-on-replica
• cleanly closing streamer connection (connection that imposes as a replica) upon completion
• on --exact-rowcount, --concurrent-rowcount now defaults true
• added validation to confirm table structure on master & replica is identical (yes, the counter case happened)
• correct (though suboptimal) behavior on enum being part of the migration key