title: protobuf backward compatibility on field name change
body: <p>If a proto's enum name is changed, is it backward compatible?</p>
  
  <p>e.g I have this initially:</p>
  
  <pre><code>enum ids {
    ID_1 = 1;
    ID_2 = 2; 
  };
  
  
  message {
    ids id = 1
  };
  </code></pre>
  
  <p>And I modify the enum definition to:</p>
  
  <pre><code>enum ids {
    ID_3 = 1;
    ID_2 = 2;
  };
  </code></pre>
  
  <p>Are old proto messages with ID_1 compatible with the new parser compiled from the message that contains ID_3?</p>