Merge branch 'kw/commit-keep-index-when-pre-commit-is-not-run'

"git commit" used to discard the index and re-read from the filesystem just in case the pre-commit hook has updated it in the middle; this has been optimized out when we know we do not run the pre-commit hook. * kw/commit-keep-index-when-pre-commit-is-not-run: commit: skip discarding the index if there is no pre-commit hook