backport.pl: Rewrite the --help output from scratch.
backport.pl: Rewrite the --help output from scratch.

* tools/dist/backport.pl
  (usage): Revamp.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1499563 13f79535-47bb-0310-9956-ffa450edef68

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