title: 'RepeatedScalarFieldContainer' object has no attribute 'add'
body: <p>I want to build a protobuf message on protobuf's API on python.
  Here is my proto file. But I can't add "D" in my code.</p>
  
  <pre><code>package pkg;
  message A
  {
      repeated B b = 1;
  }
  message B
  {
      C c = 1;
  }
  message C
  {
      enum D {
          OPTION1 = 1;
          OPTION2 = 2;
      }
      repeated D d = 1;
  
  }
  </code></pre>
  
  <p>Here is my python code.</p>
  
  <pre><code>    my_A = A()
      my_B = my_A.b.add()
      my_B.c.add(D.OPTION1)
  </code></pre>
  
  <p>Here is what i got:</p>
  
  <p><strong>AttributeError: 'RepeatedScalarFieldContainer' object has no attribute 'add'</strong></p>