Added convenience methods for to/from xml and json
diff --git a/src/ProtocolBuffers/GeneratedBuilder.cs b/src/ProtocolBuffers/GeneratedBuilder.cs
index 4d4be21..94948e4 100644
--- a/src/ProtocolBuffers/GeneratedBuilder.cs
+++ b/src/ProtocolBuffers/GeneratedBuilder.cs
@@ -49,7 +49,7 @@
     /// </summary>

     public abstract class GeneratedBuilder<TMessage, TBuilder> : AbstractBuilder<TMessage, TBuilder>

         where TMessage : GeneratedMessage<TMessage, TBuilder>

-        where TBuilder : GeneratedBuilder<TMessage, TBuilder>

+        where TBuilder : GeneratedBuilder<TMessage, TBuilder>, new()

     {

         /// <summary>

         /// Returns the message being built at the moment.