[PATCH] revert: don't backup if no files reverted in interactive mode (issue4793)

[Yuya Nishihara]

On Fri, 1 Jul 2016 11:26:35 -0700, Sean Karlage wrote:
> # HG changeset patch
> # User skarlage <skarlage at fb.com>
> # Date 1467301099 25200
> #      Thu Jun 30 08:38:19 2016 -0700
> # Node ID 15417d1e4d3c1d3fb0108df57cf9ecff4bf50357
> # Parent  ecbbf4d56ee82b48fe4fa19d68056b9d17eff570
> revert: don't backup if no files reverted in interactive mode (issue4793)

This looks good to me, but there might be a pitfall I couldn't notice. So
marked as 2nd Review Requested.