Fix System.ServiceModel.Description.ClientCredentials..ctor

The protected constructor and MakeReadOnly() method does not properly clone the
_clientCertificate, _serverCertificate fields

Fixes dotnet#458

src/System.Private.ServiceModel/src/System/ServiceModel/Description/ClientCredentials.cs

@@ -27,11 +27,29 @@ protected ClientCredentials(ClientCredentials other)
                 throw DiagnosticUtility.ExceptionUtility.ThrowHelperArgumentNull("other");
             if (other._userName != null)
                 _userName = new UserNamePasswordClientCredential(other._userName);
+            if (other._clientCertificate != null)
+                _clientCertificate = new X509CertificateInitiatorClientCredential(other._clientCertificate);
+            if (other._serviceCertificate != null)
+                _serviceCertificate = new X509CertificateRecipientClientCredential(other._serviceCertificate);
             if (other._httpDigest != null)
                 _httpDigest = new HttpDigestClientCredential(other._httpDigest);
             _isReadOnly = other._isReadOnly;
         }
 
+        public UserNamePasswordClientCredential UserName
+        {
+            get
+            {
+                if (_userName == null)
+                {
+                    _userName = new UserNamePasswordClientCredential();
+                    if (_isReadOnly)
+                        _userName.MakeReadOnly();
+                }
+                return _userName;
+            }
+        }
+
         public X509CertificateInitiatorClientCredential ClientCertificate
         {
             get
@@ -60,21 +78,6 @@ public X509CertificateRecipientClientCredential ServiceCertificate
             }
         }
 
-        public UserNamePasswordClientCredential UserName
-        {
-            get
-            {
-                if (_userName == null)
-                {
-                    _userName = new UserNamePasswordClientCredential();
-                    if (_isReadOnly)
-                        _userName.MakeReadOnly();
-                }
-                return _userName;
-            }
-        }
-
-
         public WindowsClientCredential Windows
         {
             get
@@ -177,8 +180,18 @@ public virtual void ApplyClientBehavior(ServiceEndpoint serviceEndpoint, ClientR
         // RC0 workaround to freeze credentials when the channel factory is opened
         internal void MakeReadOnly()
         {
+            _isReadOnly = true; 
+
+            if (_clientCertificate != null)
+                _clientCertificate.MakeReadOnly();
+            if (_serviceCertificate != null)
+                _serviceCertificate.MakeReadOnly();
+            if (_userName != null)
+                _userName.MakeReadOnly();
             if (_windows != null)
                 _windows.MakeReadOnly();
+            if (_httpDigest != null)
+                _httpDigest.MakeReadOnly();
         }
     }
 }