title: No serializer defined for System.Version in protobuf-net
body: <p>After updating to the latest protobuf-net (2.0.0.601) I now get an exception when trying to serialize a value of type System.Version.</p>
  
  <pre><code>[ProtoContract(SkipConstructor=true)]   
  public class ServerLoginInfo
  {
      [ProtoMember(1)]
      public Version ServerVersion { get; set; }
  }
  </code></pre>
  
  <p>This used to work fine in 2.0.0.480 without doing anything special.</p>
  
  <p>Is it possible to get it working in the new version or is my only option to rollback to the old version?</p>
  
  <p>(I also need the serialization/deserialization to be backwards compatible with the old protobuf-net version.)</p>