Implement BrowserLikeRedirectAgent, a redirect agent that treats HTTP 301 and 302 like HTTP 303 for non-HEAD/GET requests, changing the method to GET before proceeding. refs #5434

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/branches/browser-like-redirect-agent-5434@37857 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb