non-standard things in the gnu stl

[Gabriel Dos Reis]

Uwe Sassenberg <uwe@sci-d-vis.com> writes:

| Here is a brief description of the problem:
| 
| ------------8<------------
| 
| There is no difference in the definition of std::set<T>::iterator and
| std::set<T>::const_iterator. 

   http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#103

| As a consequence, there is only a method
| 
| iterator begin() const;
| 
| but the Standard requires two methods
| 
| const_iterator begin() const;
| iterator begin();

-- Gaby