'warning's was improperly requiring that a command-line Warning category be
both a subclass of Warning and a subclass of types.ClassType.  The latter is no
longer true thanks to new-style exceptions.

Closes bug #1510580.  Thanks to AMK for the test.
diff --git a/Misc/NEWS b/Misc/NEWS
index d02f40f..ae1963f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -16,6 +16,10 @@
 Library
 -------
 
+- Bug #1510580: The 'warnings' module improperly required that a Warning
+  category be either a types.ClassType and a subclass of Warning.  The proper
+  check is just that it is a subclass with Warning as the documentation states.
+
 - The compiler module now correctly compiles the new try-except-finally
   statement (bug #1509132).