Allow forcing HTTP protocol version

	If the version is manually set, ignore the version from the service
	point when set.

	Fixes bug #668199.

mcs/class/System/System.Net/HttpWebRequest.cs

@@ -76,6 +76,7 @@ namespace System.Net
 		bool preAuthenticate;
 		bool usedPreAuth;
 		Version version = HttpVersion.Version11;
+		bool force_version;
 		Version actualVersion;
 		IWebProxy proxy;
 		bool sendChunked;
@@ -517,6 +518,7 @@ namespace System.Net
 				if (value != HttpVersion.Version10 && value != HttpVersion.Version11)
 					throw new ArgumentException ("value");
 
+				force_version = true;
 				version = value; 
 			}
 		}
@@ -1191,7 +1193,7 @@ namespace System.Net
 									actualUri.PathAndQuery);
 			}
 			
-			if (servicePoint.ProtocolVersion != null && servicePoint.ProtocolVersion < version) {
+			if (!force_version && servicePoint.ProtocolVersion != null && servicePoint.ProtocolVersion < version) {
 				actualVersion = servicePoint.ProtocolVersion;
 			} else {
 				actualVersion = version;