Fix for 303 Redirects

303 Redirects are required to be executed with a GET request regardless of the method used in the original request.  See http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html.  Guzzle currently only switches the method to GET for 300-302.  This update corrects handling of 303 redirects to always use GET.  The strict redirects options has no bearing on this behavior.  

The following blog post gives a nice explanation of the various redirect methods, their intended behavior, and what real browsers actually do.  http://blogs.msdn.com/b/ieinternals/archive/2011/08/19/understanding-the-impact-of-redirect-response-status-codes-on-http-methods-like-head-get-post-and-delete.aspx