Make motion-yaml retain original YAML if object being re-serialized has not been modified.

yaml.rb

class << YAML
  alias _load load
  private :_load
  def load(yaml)
    hash = _load(yaml)
    unless hash.nil?
      hash.instance_variable_set(:@original_yaml, yaml)
      hash.instance_variable_set(:@original_parsed_yaml, hash)
    end
    hash
  end

  alias _dump dump
  private :_dump
  def dump(object)
    unless object.nil?
      object.instance_eval do
        if @original_parsed_yaml == self
          @original_yaml
        else
          YAML.send(:_dump, self)
        end
      end
    end
  end
end