Merge branch 'ma/shortlog-revparse'

"git shortlog cruft" aborted with a BUG message when run outside a
Git repository.  The command has been taught to complain about
extra and unwanted arguments on its command line instead in such a
case.

* ma/shortlog-revparse:
  shortlog: disallow left-over arguments outside repo
  shortlog: add usage-string for stdin-reading
  git-shortlog.txt: reorder usages