Critical Description
Implement separate gflag (perhaps --backup_max_incremental_age_sec) for non-snapshot history retention separate from --tablet_history_max_age_sec; Actual retention will be maximum of these two flags, but regular scans still may only scan after --tablet_history_max_age_sec. This makes it possible to implement snapshots in future releases by retiring or changing the semantics of the --tablet_history_max_age_sec flag.
Overall this help support backup jobs that run for an extended period of time.