Do not mention 2.7+ behavior in the 2.6 docs.

Doc/library/threading.rst

@@ -693,11 +693,7 @@ An event object manages an internal flag that can be set to true with the
       floating point number specifying a timeout for the operation in seconds
       (or fractions thereof).
 
-      This method returns the internal flag on exit, so it will always return
-      ``True`` except if a timeout is given and the operation times out.
-
-      .. versionchanged:: 2.7
-         Previously, the method always returned ``None``.
+      This method always returns ``None``.
 
 
 .. _timer-objects: