Merge branch 'en/diffcore-rename'

Merge branch 'en/diffcore-rename'

Performance optimization work on the rename detection continues.

* en/diffcore-rename:
  merge-ort: call diffcore_rename() directly
  gitdiffcore doc: mention new preliminary step for rename detection
  diffcore-rename: guide inexact rename detection based on basenames
  diffcore-rename: complete find_basename_matches()
  diffcore-rename: compute basenames of source and dest candidates
  t4001: add a test comparing basename similarity and content similarity
  diffcore-rename: filter rename_src list when possible
  diffcore-rename: no point trying to find a match better than exact