Issue #4129: Documentation notes for int -> Py_ssize_t changes.

Doc/c-api/allocation.rst

@@ -33,6 +33,10 @@ Allocating Objects on the Heap
    This does everything :cfunc:`PyObject_Init` does, and also initializes the
    length information for a variable-size object.
 
+   .. versionchanged:: 2.5
+      This function used an :ctype:`int` type for *size*. This might require
+      changes in your code for properly supporting 64-bit systems.
+
 
 .. cfunction:: TYPE* PyObject_New(TYPE, PyTypeObject *type)
 
@@ -54,6 +58,10 @@ Allocating Objects on the Heap
    fields into the same allocation decreases the number of allocations,
    improving the memory management efficiency.
 
+   .. versionchanged:: 2.5
+      This function used an :ctype:`int` type for *size*. This might require
+      changes in your code for properly supporting 64-bit systems.
+
 
 .. cfunction:: void PyObject_Del(PyObject *op)