Add note about int as abstract base class.

pep-3000.txt

@@ -109,6 +109,7 @@ Atomic Types
 ============
 
 * Remove distinction between int and long types [1]_
+  (int may become an abstract base type, with short and long subtypes.)
 * Make all strings be Unicode, and have a separate bytes() type [1]_
 * Return iterators instead of lists where appropriate for atomic type methods
   (e.g. ``dict.keys()``, ``dict.values()``, ``dict.items()``, etc.); iter*