SHA-256 is Git's next hash algorithm. The world is still basically stuck
on SHA-1 with git, but shouldn't be. We can at least do our part to get
ready.
On the C++ implementation side, only a little bit of generalization was
needed, and that was fairly straight-forward. The tests (unit and
system) were actually bigger, and care was taken to make sure they were
all cover both algorithms equally.
This seems to be the way to do it now, even though I can't run them
without setting at least one env var.
I'll only fix shellcheck for now. Don't shoot the messenger.
It isn't quite clear to me why the previous commit masked this problem,
but I'm glad shellcheck has an effect or more effect now.
