Add callable() to the list of functions returning 'bool'.

pep-0285.txt

@@ -137,10 +137,11 @@ Specification
     result will be changed to return False or True instead of 0 or 1.
     In particular, this affects comparisons (<, <=, ==, !=, >, >=, is,
     is not, in, not it), the unary operator 'not', and built-in
-    functions like hasattr(), isinstance() and issubclass(), the dict
-    method has_key(), string methods endswith(), isalnum(), isalpha(),
-    isdigit(), islower(), isspace(), istitle(), isupper(), and
-    startswith(), and the closed attribute of file objects.
+    functions like callable(), hasattr(), isinstance() and
+    issubclass(), the dict method has_key(), string methods
+    endswith(), isalnum(), isalpha(), isdigit(), islower(), isspace(),
+    istitle(), isupper(), and startswith(), and the closed attribute
+    of file objects.
 
     Note that subclassing from int means that True+1 is valid and
     equals 2, and so on.  This is important for backwards