Merge branch 'en/ort-perf-batch-9'

The ort merge backend has been optimized by skipping irrelevant
renames.

* en/ort-perf-batch-9:
  diffcore-rename: avoid doing basename comparisons for irrelevant sources
  merge-ort: skip rename detection entirely if possible
  merge-ort: use relevant_sources to filter possible rename sources
  merge-ort: precompute whether directory rename detection is needed
  merge-ort: introduce wrappers for alternate tree traversal
  merge-ort: add data structures for an alternate tree traversal
  merge-ort: precompute subset of sources for which we need rename detection
  diffcore-rename: enable filtering possible rename sources

diff --cc diffcore-rename.c
Simple merge

diff --cc diffcore.h
Simple merge

diff --cc merge-ort.c
Simple merge

diff --cc t/t6423-merge-rename-directories.sh
Simple merge