Merge branch 'dw/check-ignore-sans-index'

"git check-ignore" follows the same rule as "git add" and "git status" in that the ignore/exclude mechanism does not take effect on paths that are already tracked. With "--no-index" option, it can be used to diagnose which paths that should have been ignored have been mistakenly added to the index. * dw/check-ignore-sans-index: check-ignore: Add option to ignore index contents