SF #829941, update tutorial, built-in types can be base classes since 2.2

Doc/tut/tut.tex

@@ -3550,8 +3550,8 @@ method function is declared with an explicit first argument
 representing the object, which is provided implicitly by the call.  As
 in Smalltalk, classes themselves are objects, albeit in the wider
 sense of the word: in Python, all data types are objects.  This
-provides semantics for importing and renaming.  But, just like in
-\Cpp{} or Modula-3, built-in types cannot be used as base classes for
+provides semantics for importing and renaming.  Unlike 
+\Cpp{} and Modula-3, built-in types can be used as base classes for
 extension by the user.  Also, like in \Cpp{} but unlike in Modula-3, most
 built-in operators with special syntax (arithmetic operators,
 subscripting etc.) can be redefined for class instances.