Finish http refactoring. Test suite passing.
* bzrlib/transport/http/_pycurl.py:
Replaces _real_abspath by _unqualified_abspath.
* bzrlib/transport/http/_urllib.py:
Replaces _real_abspath by _unqualified_abspath.
* bzrlib/transport/http/__init__.py:
(HttpTransportBase.abspath): Deleted.
(HttpTransportBase._unqualified_abspath): Kind of _remote_path for
hhtp, replaces _real_abspath.
* bzrlib/tests/test_http.py:
(TestHttpTransportUrls.test_invalid_http_urls): Delete the test
for directories, we are not listable anyway.