Merge branch 'rs/parseopt-short-help'

Make "-h" command line option work more consistently in all commands.

* rs/parseopt-short-help:
  show-ref: stop using PARSE_OPT_NO_INTERNAL_HELP
  grep: stop using PARSE_OPT_NO_INTERNAL_HELP
  parse-options: allow -h as a short option
  parse-options: inline parse_options_usage() at its only remaining caller
  parse-options: deduplicate parse_options_usage() calls