Merge branch 'mm/die-with-dashdash-help'

When the user gives an argument that can be taken as both a revision name and a pathname without disambiguating with "--", we used to give a help message "Use '--' to separate". The message has been clarified to show where that '--' goes on the command line. * mm/die-with-dashdash-help: setup: clarify error messages for file/revisions ambiguity