title: WebRequest.RegisterPrefix for http:// returns true, doesn't work
body: <p>I'm trying to use <a href="http://msdn.microsoft.com/en-us/library/system.net.webrequest.registerprefix%28v=VS.95%29.aspx" rel="nofollow"><code>WebRequest.RegisterPrefix</code></a> to register a decorator <a href="http://msdn.microsoft.com/en-us/library/system.net.iwebrequestcreate%28v=VS.95%29.aspx" rel="nofollow"><code>IWebRequestCreate</code></a> implementation with the intention being to add "debug" scenarios (like emulating different connectivity scenarios). </p>
  
  <p>I'm using the Mango beta 2 SDK and the <code>RegisterPrefix</code> method always returns true when used with "http://" as a prefix (or "http" for that matter), but the registered IWebRequestCreate instance is not being used.</p>
  
  <p>I can see from the documentation that it should return false for duplicates, but it doesn't seem to be functioning as documented.</p>
  
  <p>Is there any other way of achieving what I'm after in a way that is transparent to consumers?</p>