std::vector<T>::const_reverse_iterator

[Joe Buck]

> > But shouldn't there be a conversion from T::reverse_iterator to
> > T::const_reverse_iterator, which would make this work?
> 
> I don't see one in the standard. Do you?

Sigh.  Defect report time.

For reasonable code sequences to work, containers need to have conversions
between non-const iterators and the corresponding const_iterator.  I
could have sworn that I read language like that before (so I had
vaguely assumed it was in the standard somewhere), but evidently it is
not.