Merge branch 'en/remerge-diff'

"git log --remerge-diff" shows the difference from mechanical merge result and the result that is actually recorded in a merge commit. * en/remerge-diff: diff-merges: avoid history simplifications when diffing merges merge-ort: mark conflict/warning messages from inner merges as omittable show, log: include conflict/warning messages in --remerge-diff headers diff: add ability to insert additional headers for paths merge-ort: format messages slightly different for use in headers merge-ort: mark a few more conflict messages as omittable merge-ort: capture and print ll-merge warnings in our preferred fashion ll-merge: make callers responsible for showing warnings log: clean unneeded objects during `log --remerge-diff` show, log: provide a --remerge-diff capability