Catch spurious exceptions (python-2.6) when SocketServer is shut down.

* bzrlib/tests/test_http.py:
(TestProxyHttpServer.proxied_in_env,
TestProxyHttpServer.not_proxied_in_env): Revert expected and
actual expressions to conform with bzr rules.

* bzrlib/tests/http_server.py:
(HttpServer.__repr__): Added for debug purposes.
(HttpServer._http_start): Catch spurious exceptions when running
with python-2.6.