Windows tests cleanup.

* bzrlib/tests/HTTPTestUtil.py: 
(BadStatusRequestHandler.parse_request): Catch more exceptions.

* bzrlib/tests/test_http.py:
(RecordingServer._accept_read_and_reply): Catch socket.error in
case client close the socket early.
(TestPost, TestPost_urllib, TestPost_pycurl): Separate urllib and
pycurl tests so that we can test without pycurl installed.

* bzrlib/tests/blackbox/test_mv.py: 
Import TestSkipped.