Fully converted over to ICodedOutputStream for all WriteTo derivations
diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestCSharpOptionsProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestCSharpOptionsProtoFile.cs
index aaca1b9..9cc59a2 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestCSharpOptionsProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestCSharpOptionsProtoFile.cs
@@ -115,7 +115,7 @@
       }

     }

     

-    public override void WriteTo(pb::CodedOutputStream output) {

+    public override void WriteTo(pb::ICodedOutputStream output) {

       int size = SerializedSize;

       if (HasNormal) {

         output.WriteString(1, "normal", Normal);