bpo-30500: urllib: Simplify splithost by calling into urlparse. (#1849) (#2294)

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``.
(cherry picked from commit 90e01e50ef8a9e6c91f30d965563c378a4ad26de)
diff --git a/Lib/urllib.py b/Lib/urllib.py
index c3c8ef4..d85504a 100644
--- a/Lib/urllib.py
+++ b/Lib/urllib.py
@@ -1093,8 +1093,7 @@
     """splithost('//host[:port]/path') --> 'host[:port]', '/path'."""
     global _hostprog
     if _hostprog is None:
-        import re
-        _hostprog = re.compile('^//([^/?]*)(.*)$')
+        _hostprog = re.compile('//([^/#?]*)(.*)', re.DOTALL)
 
     match = _hostprog.match(url)
     if match: