urllib: Simplify splithost by calling into urlparse. (#1849)

urllib: Simplify splithost by calling into urlparse. (#1849)

The current regex based splitting produces a wrong result. For example::

  http://abc#@def

Web browsers parse that URL as ``http://abc/#@def``, that is, the host
is ``abc``, the path is ``/``, and the fragment is ``#@def``.