This instance will be upgraded to Heptapod 0.19.0rc2 on 2021-01-18 at 11:00 UTC+1 (a few minutes of downtime)

WIP rhg status: implement recheck with actual file content [skip ci]

Lots of TODOs and exciting opportunities for refactoring.

Notably, comparison of permissions and similar metadata is not

At this point, for clarity in experimentations, the modified and
clean statuses are displayed as `M (rechecked)` and `C (rechecked)`
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