- don't close the fp, since that appears to also close the socket
    - join the original url with the redirect reponse to deal with
      relative redirect URL

wrap two socket ops in try/except to turn them into URLErrors, so that
client code need only catch one exception.

in HTTPError.__del__ only close fp if fp is not None

style changes:
    - use f(*args) instead of apply(f, args)
    - use __super_init instead of super.__init__(self, ...)