Fix bug #9155. Problem with delegate class.

Problem was that a simple class like:

    class X < DelegateClass(Integer)
      def initialize(value)
        value = Integer(value)
        super(value)
      end
    end

would fail because Integer would call method_missing of SimpleDelegate, but that would raise an exception since the object to delegate to is not yet set (it will be when super is called).

/cc @nobu