download: don't use splitport and splituser

They are deprecated since Python 3.8

Rebase instructions:
- split and fixup commits
    171c2459
    c9e9b267

src/zc/buildout/download.py

@@ -21,13 +21,13 @@ except ImportError:
 try:
     # Python 3
     from urllib.error import HTTPError
-    from urllib.request import Request, splitport, splituser, urlopen
+    from urllib.request import Request, urlopen
     from urllib.parse import urlparse, urlunparse
 except ImportError:
     # Python 2
     from urlparse import urlparse
     from urlparse import urlunparse
-    from urllib2 import HTTPError, Request, splitport, splituser, urlopen
+    from urllib2 import HTTPError, Request, urlopen
 
 from zc.buildout.easy_install import realpath
 from base64 import b64encode
@@ -271,14 +271,15 @@ class Download(object):
             return '%s:%s' % (url_host, url_port)
 
     def urlretrieve(self, url, tmp_path):
-        scheme, netloc, path, params, query, frag = urlparse(url)
+        parsed_url = urlparse(url)
         req = url
-        while scheme in ('http', 'https'): # not a loop
-            auth, host = splituser(netloc)
-            if auth:
-                url = urlunparse((scheme, host, path, params, query, frag))
+        while parsed_url.scheme in ('http', 'https'): # not a loop
+            auth_host = parsed_url.netloc.rsplit('@', 1)
+            if len(auth_host) > 1:
+                auth = auth_host[0]
+                url = parsed_url._replace(netloc=auth_host[1]).geturl()
             else:
-                auth = netrc.authenticators(splitport(host)[0])
+                auth = netrc.authenticators(parsed_url.hostname)
                 if not auth:
                     break
                 auth = '{0}:{2}'.format(*auth)