Fixed a warning, when lexical cast is used to convert a boost::ulong_long_type to a string.

[SVN r37082]

include/boost/lexical_cast.hpp

@@ -505,7 +505,7 @@ namespace boost
 
                 --left;
                 --finish;
-                int const digit = n % 10;
+                int const digit = static_cast<int const>(n % 10);
                 int const cdigit = digit + lcast_char_constants<CharT>::zero;
                 *finish = static_cast<char>(cdigit);
                 n /= 10;