Minor regex fixes for VC6 (Added some boost:: qualifies to work around lack or Koenig lookup).

[SVN r8238]

demo/snippets/snip7.cpp

@@ -69,7 +69,7 @@ void class_index::IndexClasses(const std::string& file)
    end = file.end();
    base = start;
    class_index::grep_callback_type cl = &(this->grep_callback);
-   regex_grep(cl,
+   boost::regex_grep(cl,
             start,
             end,
             expression);
@@ -118,3 +118,4 @@ int main(int argc, const char** argv)
 }
 
 
+