proxy helper code refactor.

framework/src/Volo.Abp.Core/Volo/Abp/DynamicProxy/ProxyHelper.cs

@@ -5,13 +5,14 @@ namespace Volo.Abp.DynamicProxy
 {
     public static class ProxyHelper
     {
+        private const string ProxyNamespace = "Castle.Proxies";
         /// <summary>
         /// Returns dynamic proxy target object if this is a proxied object, otherwise returns the given object. 
         /// It supports Castle Dynamic Proxies.
         /// </summary>
         public static object UnProxy(object obj)
         {
-            if (obj.GetType().Namespace != "Castle.Proxies")
+            if (obj.GetType().Namespace != ProxyNamespace)
             {
                 return obj;
             }