Function read_recorded_callback_checkpoints 

pub fn read_recorded_callback_checkpoints(path: &Path) -> Result<bool, String>

Read only whether a preemption record file carries callback checkpoints (Config::annotated_priority_replay), as read_recorded_epoch reads the epoch. A record without the field, older or made without chaos recording, carries none. Detcore validates the whole record, checkpoints included, when it loads it for the run.