More win in serialization scenarios wrt curr.cult.

If the object will be serialized via ToString, it will be checked
whether the object implements IFormattable and then a CultureInvariant
ToString overload is called.

Author: flq

src/ServiceStack.Text/Common/ITypeSerializer.cs

@@ -20,6 +20,7 @@ internal interface ITypeSerializer
         void WriteObjectString(TextWriter writer, object value);
         void WriteException(TextWriter writer, object value);
         void WriteString(TextWriter writer, string value);
+        void WriteFormattableObjectString(TextWriter writer, object value);
         void WriteDateTime(TextWriter writer, object oDateTime);
         void WriteNullableDateTime(TextWriter writer, object dateTime);
         void WriteDateTimeOffset(TextWriter writer, object oDateTimeOffset);

src/ServiceStack.Text/Common/JsWriter.cs

@@ -323,6 +323,9 @@ public WriteObjectDelegate GetValueTypeToStringMethod(Type type)
                     ? (WriteObjectDelegate)Serializer.WriteEnumFlags
                     : Serializer.WriteEnum;
 
+            if (type.HasInterface(typeof (IFormattable)))
+                return Serializer.WriteFormattableObjectString;
+
             return Serializer.WriteObjectString;
         }
 

src/ServiceStack.Text/Json/JsonTypeSerializer.cs

@@ -108,6 +108,12 @@ public void WriteObjectString(TextWriter writer, object value)
             JsonUtils.WriteString(writer, value != null ? value.ToString() : null);
         }
 
+        public void WriteFormattableObjectString(TextWriter writer, object value)
+        {
+            var formattable = value as IFormattable;
+            JsonUtils.WriteString(writer, formattable != null ? formattable.ToString(null, CultureInfo.InvariantCulture) : null);
+        }
+
         public void WriteException(TextWriter writer, object value)
         {
             WriteString(writer, ((Exception)value).Message);

src/ServiceStack.Text/Jsv/JsvTypeSerializer.cs

@@ -88,7 +88,13 @@ public void WriteString(TextWriter writer, string value)
 			writer.Write(value.EncodeJsv());
 		}
 
-		public void WriteDateTime(TextWriter writer, object oDateTime)
+	    public void WriteFormattableObjectString(TextWriter writer, object value)
+	    {
+	        var f = (IFormattable)value;
+	        writer.Write(f.ToString(null,CultureInfo.InvariantCulture).EncodeJsv());
+	    }
+
+	    public void WriteDateTime(TextWriter writer, object oDateTime)
 		{
 			writer.Write(DateTimeSerializer.ToShortestXsdDateTimeString((DateTime)oDateTime));
 		}