Feature request: print warnings during --dry-run

[nmay231]

This is just a side-thought from #867.

It might be helpful to print warnings during a --dry-run for mistakes like using sha256("file/path.txt") instead of sha256_file("file/path.txt"). Don't know how common or reasonable this is, but it's a thought. *shrug*

[casey]

I think it's not possible to detect an error like sha256("file/path.txt"), since you might actually want the hash of that string. Anything that is detectable should get a warning, and that should definitely printed during --dry-run.