Merge branch 'en/merge-ort-2'

More "ORT" merge strategy.

* en/merge-ort-2:
  merge-ort: add modify/delete handling and delayed output processing
  merge-ort: add die-not-implemented stub handle_content_merge() function
  merge-ort: add function grouping comments
  merge-ort: add a paths_to_free field to merge_options_internal
  merge-ort: add a path_conflict field to merge_options_internal
  merge-ort: add a clear_internal_opts helper
  merge-ort: add a few includes