[fix #203] fix a bug in super which fails to look up method in method which called by super

The 'super' saves the calling status (caller class, selector, etc).
At twice 'super' calling, look up wrong class.

The following sequence had executed.

- Base (Super class)
- Foo (Inherited Base)

1. Foo#bar -- super --> look up super class of Foo (Base)
2. Foo#bar -- super --> look up super class of Base

----

class Base
  def bar(args)
    $result << args.first
    if args = args[1..-1]
      obj = Foo.new
      obj.bar(args)
    end
  end
end

class Foo < Base
  def bar(args)
    $result << "a"
    super
  end
end

$result = []
obj = Foo.new
obj.bar(%w{1 2 3})
p $result