def get_one_gem_name
    args = options[:args]

    if args.nil? or args.empty? then
      raise Gem::CommandLineError,
            "Please specify a gem name on the command line (e.g. gem build GEMNAME)"
    end

    if args.size > 1 then
      raise Gem::CommandLineError,
            "Too many gem names (#{args.join(', ')}); please specify only one"
    end

    args.first
  end
#
Get a single gem name from the command line.  Fail if there is no gem name
or if there is more than one gem name given.