backport.pl: handle SIGINT (^C).
backport.pl: handle SIGINT (^C).

* tools/dist/backport.pl
  (maybe_revert): New helper.
  (main): Break out the last part into the helper, and install it as a signal
    handler, too.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1499093 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion