Merge branch 'maint'

Merge branch 'maint'

* maint:
  blame: correctly handle a path that used to be a directory
  add -i: do not dump patch during application
  Update draft release notes for 1.6.3.2
  grep: fix colouring of matches with zero length
  Documentation: teach stash/pop workflow instead of stash/apply
  Change xdl_merge to generate output even for null merges
  t6023: merge-file fails to output anything for a degenerate merge