Fix for public constructor on messages
diff --git a/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs b/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
index 70222e0..76cb1fe 100644
--- a/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
+++ b/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
@@ -126,6 +126,7 @@
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]

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

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

+    private CSharpFileOptions() { }

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

     private static readonly string[] _cSharpFileOptionsFieldNames = new string[] { "add_serializable", "cls_compliance", "code_contracts", "expand_namespace_directories", "file_extension", "ignore_google_protobuf", "multiple_files", "namespace", "nest_classes", "output_directory", "public_classes", "service_generator_type", "umbrella_classname", "umbrella_namespace" };

     private static readonly uint[] _cSharpFileOptionsFieldTags = new uint[] { 72, 64, 48, 56, 1770, 1792, 32, 10, 40, 1786, 24, 1800, 18, 1778 };

@@ -911,6 +912,7 @@
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]

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

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

+    private CSharpFieldOptions() { }

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

     private static readonly string[] _cSharpFieldOptionsFieldNames = new string[] { "property_name" };

     private static readonly uint[] _cSharpFieldOptionsFieldTags = new uint[] { 10 };

@@ -1151,6 +1153,7 @@
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]

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

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

+    private CSharpServiceOptions() { }

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

     private static readonly string[] _cSharpServiceOptionsFieldNames = new string[] { "interface_id" };

     private static readonly uint[] _cSharpServiceOptionsFieldTags = new uint[] { 10 };

@@ -1391,6 +1394,7 @@
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]

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

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

+    private CSharpMethodOptions() { }

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

     private static readonly string[] _cSharpMethodOptionsFieldNames = new string[] { "dispatch_id" };

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