Refactor proxy and auth test classes. Tests failing for digest auth.
* bzrlib/transport/http/_urllib2_wrappers.py: (AbstractAuthHandler.auth_required, AbstractAuthHandler.auth_successful): Add response parameter as an authentication scheme may need additional info provided only there.
* bzrlib/tests/test_http.py: (TestAuth, TestHTTPAuth, TestProxyAuth, TestHTTPBasicAuth, TestHTTPProxyBasicAuth): Refactoring. (TestHTTPDigestAuth, TestHTTPProxyDigestAuth): New classes for digest authentication tests.
* bzrlib/tests/HttpServer.py: (TestingHTTPRequestHandler.translate_path): Handles request proxying based on a server attribute. (HttpServer): Add proxy_requests attribute.
* bzrlib/tests/HTTPTestUtil.py: (ProxyServer): Replaces FakeProxyRequestHandler now that HttpServer handles proxying based on a server attribute. (AuthRequestHandler, BasicAuthRequestHandler, AuthServer, HTTPAuthServer, ProxyAuthServer, HTTPBasicAuthServer, ProxyBasicAuthServer): Refactoring Auth servers and request handlers. (HTTPDigestAuthServer, ProxyDigestAuthServer): New classes for digest authentication.