Merge branch 'ph/parseopt-step-blame'

Merge branch 'ph/parseopt-step-blame'

* ph/parseopt-step-blame:
  revisions: refactor handle_revision_opt into parse_revision_opt.
  git-shortlog: migrate to parse-options partially.
  git-blame: fix lapsus
  git-blame: migrate to incremental parse-option [2/2]
  git-blame: migrate to incremental parse-option [1/2]
  revisions: split handle_revision_opt() from setup_revisions()
  parse-opt: add PARSE_OPT_KEEP_ARGV0 parser option.
  parse-opt: fake short strings for callers to believe in.
  parse-opt: do not print errors on unknown options, return -2 intead.
  parse-opt: create parse_options_step.
  parse-opt: Export a non NORETURN usage dumper.
  parse-opt: have parse_options_{start,end}.
  git-blame --reverse
  builtin-blame.c: allow more than 16 parents
  builtin-blame.c: move prepare_final() into a separate function.
  rev-list --children
  revision traversal: --children option