Fix IOException when the HTTP response indicates that an error occurred, as per http://developer.android.com/reference/java/net/HttpURLConnection.html
Merge pull request #18 from MediaFriendsInc2/master

Fix the error management in NetworkConnectionImpl

A bug was preventing a ConnectionException from being thrown normally
when we were getting an ErrorStream back; e.g.  when the server
responds with a 500 status code.