Fix for public constructor on messages
diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
index f1fff86..c5da553 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
@@ -71,6 +71,7 @@
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]

   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]

   public sealed partial class ImportMessage : pb::GeneratedMessage<ImportMessage, ImportMessage.Builder> {

+    private ImportMessage() { }

     private static readonly ImportMessage defaultInstance = new Builder().BuildPartial();

     private static readonly string[] _importMessageFieldNames = new string[] { "d" };

     private static readonly uint[] _importMessageFieldTags = new uint[] { 8 };