Added ToBuilder and WeakToBuilder
diff --git a/src/ProtocolBuffers/AbstractMessage.cs b/src/ProtocolBuffers/AbstractMessage.cs
index 0a69f29..11bb948 100644
--- a/src/ProtocolBuffers/AbstractMessage.cs
+++ b/src/ProtocolBuffers/AbstractMessage.cs
@@ -58,12 +58,17 @@
     public abstract UnknownFieldSet UnknownFields { get; }
     public abstract TMessage DefaultInstanceForType { get; }
     public abstract TBuilder CreateBuilderForType();
+    public abstract TBuilder ToBuilder();
     #endregion
     
     public IBuilder WeakCreateBuilderForType() {
       return CreateBuilderForType();
     }
 
+    public IBuilder WeakToBuilder() {
+      return ToBuilder();
+    }
+
     public IMessage WeakDefaultInstanceForType {
       get { return DefaultInstanceForType; }
     }