Add note that support for Python 2.4 has been dropped

CHANGES.txt

@@ -4,7 +4,7 @@
 - Support for Python 3 has been added.  On Python 3, Supervisor requires
   Python 3.2 or later.
 
-- Support for Python 2.5 has been dropped.  On Python 2, Supervisor
+- Support for Python 2.4 and 2.5 has been dropped.  On Python 2, Supervisor
   now requires Python 2.6 or later.
 
 - The ``supervisor`` package is no longer a namespace package.