astimezone() internals:  if utcoffset() returns a duration, complain if
dst() returns None (instead of treating that as 0).
diff --git a/Misc/NEWS b/Misc/NEWS
index 0034710..e786af5 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -22,6 +22,10 @@
   today() and now() now round system timestamps to the closest
   microsecond <http://www.python.org/sf/661086>.
 
+  In dt.asdatetime(tz), if tz.utcoffset(dt) returns a duration,
+  ValueError is raised of tz.dst(dt) returns None (2.3a1 treated it
+  as 0 instead).
+  
 Library
 -------