Merge branch 'rs/combine-diff-with-incompatible-options' into maint

Certain diff options are currently ignored when combined-diff is shown; mark them as incompatible with the feature. source: <220524.86v8tuvfl1.gmgdl@evledraar.gmail.com> * rs/combine-diff-with-incompatible-options: combine-diff: abort if --output is given combine-diff: abort if --ignore-matching-lines is given