Merge branch 'rs/diff-parseopts'

The way the diff machinery prepares the options array for the
parse_options API has been refactored to avoid resource leaks.

* rs/diff-parseopts:
  diff: remove parseopts member from struct diff_options
  diff: use add_diff_options() in diff_opt_parse()
  diff: factor out add_diff_options()

diff --cc diff.c
Simple merge

diff --cc diff.h
Simple merge