[boost] thread lib patch

From: François Dumont (francois.cppdevs_at_[hidden])
Date: 2005-01-08 03:00:30

Using MSVC6, STLport 5.0 beta, february 2003 SDK under Windows XP I failed 
to build thread
library because of a missing include. In read_write_mutex.cpp, tchar.h
contains _sntprintf macro definition but not the functions definition hidden
behind this macro. Those are in stdio.h. Maybe this file was included in a 
previous version of STLport but it is not anymore.

I am also surprised that those files are included if BOOST_HAS_WINTHREADS is 
defined and symbos coming from them are used if WINVER is defined. Isn't 
there a little inconsistency?

Bests