Merge pull request AuthorizeNet#137 from sunnyrajrathod/future

- Adding Changes from https://github.com/AuthorizeNet/sdk-dotnet/pull…

Author: Sunny Raj Rathod

Authorize.NET/CIM/CustomerGateway.cs

@@ -20,7 +20,9 @@ public class CustomerGateway : ICustomerGateway {
         /// <param name="apiLogin">The API login.</param>
         /// <param name="transactionKey">The transaction key.</param>
         /// <param name="mode">Test or Live.</param>
-        public CustomerGateway(string apiLogin, string transactionKey, ServiceMode mode) {
+        /// <param name="validationMode">None, Test, or Live.</param>
+        public CustomerGateway(string apiLogin, string transactionKey, ServiceMode mode, validationModeEnum? validationMode = null)
+        {
 
             if (mode == ServiceMode.Live) {
                 _gateway = new HttpXmlUtility(ServiceMode.Live, apiLogin, transactionKey);
@@ -29,6 +31,10 @@ public CustomerGateway(string apiLogin, string transactionKey, ServiceMode mode)
                 _gateway = new HttpXmlUtility(ServiceMode.Test, apiLogin, transactionKey);
                 _mode = validationModeEnum.testMode;
             }
+            if (validationMode.HasValue)
+            {
+                _mode = validationMode.Value;
+            }
         }
         /// <summary>
         /// Initializes a new instance of the <see cref="CustomerGateway"/> class.