message: build system: show diff of why we're not pushing
diff: @@ -20,7 +20,7 @@ GIT_VERSION=$(./git-version)
  if [[ "$GIT_VERSION" == *dirty ]]; then
  echo "Won't push from a dirty git repo. Commit your changes before you push."
  echo "Changes:"
  - git status --porcelain --untracked-files no
  + git diff
  exit 1
  fi
  