Cleanup.

* bzrlib/transport/http/_urllib.py:
(HttpTransport_urllib._perform): Update RedirectRequested creation.

* bzrlib/transport/http/_pycurl.py:
(PyCurlTransport._curl_perform): Update RedirectRequested creation.

* bzrlib/tests/blackbox/test_push.py:
(RedirectingMemoryTransport.mkdir): RedirectRequested wants urls
not paths. Be more precise with the paths used too.
(TestPushRedirect.test_push_redirects_on_mkdir,
TestPushRedirect.test_push_gracefully_handles_too_many_redirects):
Use '-d' instead of chdir().

* bzrlib/push.py:
(_show_push_branch.redirected): Updated and note() added (why
wasn't it there in the first place ?).

* bzrlib/errors.py:
(RedirectRequested): Simplified now that the redirection stuff is
handled by the transport itself.