Second batch to teach the diff machinery to use the parse-options
API.

* nd/diff-parseopt-2: (21 commits)
  diff-parseopt: convert --ignore-some-changes
  diff-parseopt: convert --[no-]minimal
  diff-parseopt: convert --relative
  diff-parseopt: convert --no-renames|--[no--rename-empty
  diff-parseopt: convert --find-copies-harder
  diff-parseopt: convert -C|--find-copies
  diff-parseopt: convert -D|--irreversible-delete
  diff-parseopt: convert -M|--find-renames
  diff-parseopt: convert -B|--break-rewrites
  diff-parseopt: convert --output-*
  diff-parseopt: convert --[no-]compact-summary
  diff-parseopt: convert --stat*
  diff-parseopt: convert -s|--no-patch
  diff-parseopt: convert --name-status
  diff-parseopt: convert --name-only
  diff-parseopt: convert --patch-with-stat
  diff-parseopt: convert --summary
  diff-parseopt: convert --check
  diff-parseopt: convert --dirstat and friends
  diff-parseopt: convert --numstat and --shortstat
  ...