Merging the py3k-pep3137 branch back into the py3k branch.
No detailed change log; just check out the change log for the py3k-pep3137
branch.  The most obvious changes:

  - str8 renamed to bytes (PyString at the C level);
  - bytes renamed to buffer (PyBytes at the C level);
  - PyString and PyUnicode are no longer compatible.

I.e. we now have an immutable bytes type and a mutable bytes type.

The behavior of PyString was modified quite a bit, to make it more
bytes-like.  Some changes are still on the to-do list.
diff --git a/Lib/urllib2.py b/Lib/urllib2.py
index d7679fc..fb2c303 100644
--- a/Lib/urllib2.py
+++ b/Lib/urllib2.py
@@ -802,7 +802,7 @@
         user, pw = self.passwd.find_user_password(realm, host)
         if pw is not None:
             raw = "%s:%s" % (user, pw)
-            auth = 'Basic %s' % str(base64.b64encode(raw)).strip()
+            auth = 'Basic %s' % base64.b64encode(raw).strip().decode()
             if req.headers.get(self.auth_header, None) == auth:
                 return None
             req.add_header(self.auth_header, auth)