backport.pl: Track a backwards-incompatible Perl language change.
backport.pl: Track a backwards-incompatible Perl language change.

* tools/dist/backport.pl
  (): Explicitly require version v5.10.0.  (Older Perls would not have worked
    anyway since they lack the 'say' feature which this script also requires.)
  (warnings): Disable experimental::smartmatch warnings under Perl v5.20.1
    and earlier.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1663842 13f79535-47bb-0310-9956-ffa450edef68

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