title: issue with HttpURLConnection OutputStream
body: <p>I have the following code:</p>
  
  <pre><code>String urlString = API_URL + "/checkins/add";  
              String inputdata = "v=20111111"+"&amp;venueId="+venueid+"&amp;broadcast="+broadcast+"&amp;oauth_token="+mAccessToken;  
              String content="";  
              try {  
                  URL url = new URL( urlString );
                  HttpURLConnection con = (HttpURLConnection) url.openConnection();
                  con.setRequestMethod("POST");
                  con.setDoOutput( true ); 
                  con.connect();  
  
                  Log.v("RESPONSE MESSAGE", con.getResponseMessage());
  
                  OutputStreamWriter out = new OutputStreamWriter(con.getOutputStream());  
                  out.write(inputdata);  
                  out.flush();              
  </code></pre>
  
  <p>and I am getting an error:</p>
  
  <pre><code>Exception: OutputStream unavailable because request headers have already been sent!
  </code></pre>
  
  <p>why is this?</p>