This commits includes tiny bugfix and new features listed here: * Add --re-sign flag to cert command by bronzdoc: https://github.com/rubygems/rubygems/pull/2391 * Download gems with threads. by indirect: https://github.com/rubygems/rubygems/pull/1898 git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64769 b2dd03c8-39d4-4d8f-98ff-823fe69b080e