should correct #3634; will close when merged to release

[SVN r76435]

Author: mclow

include/boost/algorithm/string/detail/case_conv.hpp

@@ -15,6 +15,8 @@
 #include <locale>
 #include <functional>
 
+#include <boost/type_traits/make_unsigned.hpp>
+
 namespace boost {
     namespace algorithm {
         namespace detail {
@@ -37,7 +39,7 @@ namespace boost {
                 CharT operator ()( CharT Ch ) const
                 {
                     #if defined(__BORLANDC__) && (__BORLANDC__ >= 0x560) && (__BORLANDC__ <= 0x564) && !defined(_USE_OLD_RW_STL)
-                        return std::tolower( Ch);
+                        return std::tolower( static_cast<typename boost::make_unsigned <CharT>::type> ( Ch ));
                     #else
                         return std::tolower<CharT>( Ch, *m_Loc );
                     #endif
@@ -57,7 +59,7 @@ namespace boost {
                 CharT operator ()( CharT Ch ) const
                 {
                     #if defined(__BORLANDC__) && (__BORLANDC__ >= 0x560) && (__BORLANDC__ <= 0x564) && !defined(_USE_OLD_RW_STL)
-                        return std::toupper( Ch);
+                        return std::toupper( static_cast<typename boost::make_unsigned <CharT>::type> ( Ch ));
                     #else
                         return std::toupper<CharT>( Ch, *m_Loc );
                     #endif