newvers.sh: Report -dirty also with staged changes

[emaste]

Summary

We add -dirty to the uname version string if the tree does not match the reported hash. Previously, staged but uncommitted changes were ignored.

[emaste]

Reported by: @naddy

[cperciva]

LGTM, but I'd wait for someone with more git expertise to confirm.

[imp]

HEAD is a universal pseudo tag that we put into the binary when we add a git tag, so it's perfect. Don't know of a better, faster way unless there's something one can do with git status, but this will certainly do until then.

Gemini says, once you boil away the fluff that

git status --porcelain <path>, but includes untracced files unless ignored. It's for general script checks for local modifications. And is the Fastest 🚀. It also handles staged files.

So that might be worth pursuing. '-uno' is what you'd add to skip untracked scanning.

[emaste]

git status --porcelain <path>, but includes untracced files unless ignored. It's for general script checks for local modifications. And is the Fastest 🚀. It also handles staged files.

That doesn't provide a useful return code though. Presumably we could check if git status --porcelain -uno returns any output, but I've already tested this change, and I found that and the git diff command have almost identical execution time.