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``.
diff --git a/Lib/urllib/parse.py b/Lib/urllib/parse.py
index 1af2906..01eb549 100644
--- a/Lib/urllib/parse.py
+++ b/Lib/urllib/parse.py
@@ -947,7 +947,7 @@
     """splithost('//host[:port]/path') --> 'host[:port]', '/path'."""
     global _hostprog
     if _hostprog is None:
-        _hostprog = re.compile('//([^/?]*)(.*)', re.DOTALL)
+        _hostprog = re.compile('//([^/#?]*)(.*)', re.DOTALL)
 
     match = _hostprog.match(url)
     if match: