Merge branch 'en/ort-harden-against-corrupt-trees'

The 'ort' merge backend has been hardened against corrupt trees by
ensuring it aborts under appropriate error conditions.

* en/ort-harden-against-corrupt-trees:
  cache-tree: fix verify_cache() to catch non-adjacent D/F conflicts
  merge-ort: abort merge when trees have duplicate entries
  merge-ort: free diff pairs queue in clear_or_reinit_internal_opts()
  merge-ort: drop unnecessary show_all_errors from collect_merge_info()
  merge-ort: propagate callback errors from traverse_trees_wrapper()

diff --cc cache-tree.c
Simple merge

diff --cc merge-ort.c
Simple merge

diff --cc t/meson.build
Simple merge