Implement a basic auth HTTP server, rewrite tests accordingly.

* bzrlib/transport/http/_urllib2_wrappers.py:
(PasswordManager.add_password, PasswordManager.find_user_password,
PasswordManager.reduce_uri): Copied from python-2.5 urllib2.py as
a stop gap. A python-2.4 compatible work must be found.
(Opener.preprocess_request): Deleted.

* bzrlib/tests/test_http.py:
(TestHTTPBasicAuth.create_transport_readonly_server): Use the
right auth HTTP server.
(TestHTTPBasicAuth.setUp): Plug the the server.
(TestHTTPBasicAuth.process_request): Deleted.

* bzrlib/tests/HTTPTestUtil.py:
(BasicAuthRequestHandler, AuthHTTPServer): New classes. Implement
basic authentication on HTTP server.