3.1 libstdc++ calls setlocale to format a number

[Teemu Torma]

I just noticed that in libstdc++ __convert_from_v template calls setlocale to 
format a number with sprintf.  

For me that does not sound a good idea, firstly because it is not MT safe 
(two threads using streams will corrupt your locale setting, or at least 
another thread is operating in the wrong "C" locale for a while), and 
setlocale is not necessarily very fast operation.  

Teemu