ensure we add punctuation as characters, patch from john moshakis

svn path=/trunk/mcs/; revision=145361

mcs/class/System.Json/System.Json/JsonReader.cs

@@ -259,7 +259,7 @@ namespace System.Json
 				case '"':
 				case '\\':
 				case '/':
-					vb.Append (c);
+					vb.Append ((char) c);
 					break;
 				case 'b':
 					vb.Append ('\x8');

mcs/class/System.ServiceModel.Web/System.Runtime.Serialization.Json/JsonReader.cs

@@ -659,7 +659,7 @@ namespace System.Runtime.Serialization.Json
 				case '"':
 				case '\\':
 				case '/':
-					vb.Append (c);
+					vb.Append ((char) c);
 					break;
 				case 'b':
 					vb.Append ('\x8');