After a stanza-upgrade it should still be possible to restore backups from the previous version and perform recovery with archive-get. However, archive-get only checked the most recent db version/id and failed.
Also clean up some issues when the same db version/id appears multiple times in the history.
Fixed by Cynthia Shang.
Reported by Clinton Adams.
Refactor storage layer to allow for new repository filesystems using drivers. (Reviewed by Cynthia Shang.)
Refactor IO layer to allow for new compression formats, checksum types, and other capabilities using filters. (Reviewed by Cynthia Shang.)
