Fixes a long-standing corner case bug around directory renames in
the merge-ort strategy.
* en/merge-dual-dir-renames-fix:
merge-ort: fix issue with dual rename and add/add conflict
merge-ort: shuffle the computation and cleanup of potential collisions
merge-ort: make a separate function for freeing struct collisions
merge-ort: small cleanups of check_for_directory_rename
t6423: add tests of dual directory rename plus add/add conflict