Merge branch 'en/merge-ort-3'

Rename detection is added to the "ORT" merge strategy.

* en/merge-ort-3:
  merge-ort: add implementation of type-changed rename handling
  merge-ort: add implementation of normal rename handling
  merge-ort: add implementation of rename collisions
  merge-ort: add implementation of rename/delete conflicts
  merge-ort: add implementation of both sides renaming differently
  merge-ort: add implementation of both sides renaming identically
  merge-ort: add basic outline for process_renames()
  merge-ort: implement compare_pairs() and collect_renames()
  merge-ort: implement detect_regular_renames()
  merge-ort: add initial outline for basic rename detection
  merge-ort: add basic data structures for handling renames

Author: gitster