When doing verifyTable on a table with writes since the last checkpoint, WiredTiger will implicitly create a new checkpoint. However, with recovery to a timestamp no implicit checkpoints are allowed. So, the validate command needs to be changed to do the following:

1. Lock the collection to validate in MODE_S
2. Signal the checkpointing thread that a new checkpoint should be created
3. Block until the new checkpoint is created

This ensures that when we call verifyTable, no dirty data exists and no implicit checkpoint will be created.