Merge branch 'nd/diff-parseopt-3'

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

* nd/diff-parseopt-3:
  diff-parseopt: convert --submodule
  diff-parseopt: convert --ignore-submodules
  diff-parseopt: convert --textconv
  diff-parseopt: convert --ext-diff
  diff-parseopt: convert --quiet
  diff-parseopt: convert --exit-code
  diff-parseopt: convert --color-words
  diff-parseopt: convert --word-diff-regex
  diff-parseopt: convert --word-diff
  diff-parseopt: convert --[no-]color
  diff-parseopt: convert --[no-]follow
  diff-parseopt: convert -R
  diff-parseopt: convert -a|--text
  diff-parseopt: convert --full-index
  diff-parseopt: convert --binary
  diff-parseopt: convert --anchored
  diff-parseopt: convert --diff-algorithm
  diff-parseopt: convert --histogram
  diff-parseopt: convert --patience
  diff-parseopt: convert --[no-]indent-heuristic

diff --cc Documentation/diff-options.txt
Simple merge

diff --cc diff.c
Simple merge