std::string exorcism hiccup

[Tony Bryant]

As recommended by listers, I've been going through my project attempting
to replace 

std::string 

with 

std::basic_string<char,std::char_traits<char>,myallocator<char> >

in order to get away from using the std::allocator, which just isn't suitable
for my project as discussed in earlier posts.

I come across a major stumbling block.

The standard exceptions use std::string internally to store their 
descriptions.

e.g. a quick persusal of std::logic_error shows that it internally stores its
description string in a (std::)string.

(However ios_base::failure stores its description in a char[256])

The locale_facet stuff is also (not surprisingly) riddled with references to
std::string.

Arrrrggghhh!!!!