Merge branch 'jk/ext-diff-with-relative' into maint-2.39

"git diff --relative" did not mix well with "git diff --ext-diff", which has been corrected. * jk/ext-diff-with-relative: diff: drop "name" parameter from prepare_temp_file() diff: clean up external-diff argv setup diff: use filespec path to set up tempfiles for ext-diff