Clarify what to use instead of callable().

pep-3100.txt

@@ -179,7 +179,7 @@ To be removed:
 
 * ``apply()``: use ``f(*args, **kw)`` instead [2]_ [done]
 * ``buffer()``: must die (use a bytes() type instead) (?) [2]_
-* ``callable()``: just call the object and catch the exception??? [2]_
+* ``callable()``: just use hasattr(x, '__call__') (?) [2]_
 * ``compile()``: put in ``sys`` (or perhaps in a module of its own) [2]_
 * ``coerce()``: no longer needed [2]_
 * ``execfile()``, ``reload()``: use ``exec()`` [2]_