Fix re-raise syntax for Python 3

pep-3333.txt

@@ -323,7 +323,7 @@ server.
                 try:
                     if headers_sent:
                         # Re-raise original exception if headers sent
-                        raise exc_info[0], exc_info[1], exc_info[2]
+                        raise exc_info[1].with_traceback(exc_info[2])
                 finally:
                     exc_info = None     # avoid dangling circular ref
             elif headers_set:
@@ -874,9 +874,9 @@ occurred.
 
 However, if ``exc_info`` is provided, and the HTTP headers have already
 been sent, ``start_response`` **must** raise an error, and **should**
-raise the ``exc_info`` tuple.  That is::
+re-raise using the ``exc_info`` tuple.  That is::
 
-    raise exc_info[0], exc_info[1], exc_info[2]
+    raise exc_info[1].with_traceback(exc_info[2])
 
 This will re-raise the exception trapped by the application, and in
 principle should abort the application.  (It is not safe for the