Previously chown() would be called even when no ownership changes were required.
In most cases changes are not required and it seems better to perform an extra stat() rather than an extra chown().
Also add unit tests for owner() since there weren't any.
Previously an error would be generated if other files were present and not owned by the PostgreSQL user. This hasn't been a big deal in practice but it could cause issues.
Also add tests to make sure the same logic applies with links to files, i.e. all other files in the directory should be ignored. This was actually working correctly, but there were no tests for it before.
This implementation should be faster because it does not stat each file. It simply assumes that most directory entries are files so attempts an unlink() first. If the entry is reported by error codes to be a directory then it attempts an rmdir().
Previously, functions with sensitive options had to be logged at trace level to avoid exposing them. Trace level logging may still expose secrets so use with caution.
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.)
