Merge pull request #534 from hartaa/master

Added conditional compilation directive around setting the HttpWebReques...

Author: haacked

RestSharp/Http.Async.cs

@@ -379,8 +379,10 @@ private HttpWebRequest ConfigureAsyncWebRequest(string method, Uri url)
 #if !PocketPC
 			webRequest.UseDefaultCredentials = UseDefaultCredentials;
 #endif
-			webRequest.PreAuthenticate = PreAuthenticate;
 
+#if !WINDOWS_PHONE && !SILVERLIGHT
+            webRequest.PreAuthenticate = PreAuthenticate;
+#endif
 			AppendHeaders(webRequest);
 			AppendCookies(webRequest);