deferred yield.rb

  def yield_placeholder(name, content = nil, &block)
    if content_for?(name)
      concat @view_flow.get(name)
    else
      if block_given?
        content = capture(&block)
      end
      concat content
    end
  end

  def yield_block(name, content = nil, &block)
    unless content_for?(name) 
      content_for(name) do
        if block_given?
          content = capture(&block)
        end
        content
      end
    end
  end