Merge branch 'jc/parseopt-command-modes'

Many commands use --dashed-option as a operation mode selector (e.g. "git tag --delete") that the user can use at most one (e.g. "git tag --delete --verify" is a nonsense) and you cannot negate (e.g. "git tag --no-delete" is a nonsense). Make it easier for users of parse_options() to enforce these restrictions. * jc/parseopt-command-modes: tag: use OPT_CMDMODE parse-options: add OPT_CMDMODE()