backport.pl: Restore cooked mode upon abnormal termination.
backport.pl: Restore cooked mode upon abnormal termination.

* tools/dist/backport.pl
  (prompt.$getchar): Restore cooked mode if ReadKey croaked.
  (signal_handler): New.
  (main): Use signal_handler() to restore cooked mode if ReadKey was
    interrupted by a SIGTERM.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1507967 13f79535-47bb-0310-9956-ffa450edef68

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