Since 2.91 JSON::PP has a bias for saving variables that look like numbers as numbers even if they were declared as strings.
Force versions to strings where needed by appending ''.
Update the json-pp-perl package on Ubuntu 18.04 to 2.97 to provide test coverage.
This provides correct matching in the event there are system-id and db-version duplicates (e.g. after reverting a pg_upgrade).
Fixed by Cynthia Shang.
Reported by Adam K. Sumner.
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.)
