fetch_specs

# File lib/bundler/rubygems_integration.rb, line 747
      def fetch_specs(source, remote, name)
        path = source + "#{name}.#{Gem.marshal_version}.gz"
        fetcher = gem_remote_fetcher
        fetcher.headers = { "X-Gemfile-Source" => remote.original_uri.to_s } if remote.original_uri
        string = fetcher.fetch_path(path)
        Bundler.load_marshal(string)
      rescue Gem::RemoteFetcher::FetchError => e
        # it's okay for prerelease to fail
        raise e unless name == "prerelease_specs"
      end