Added more () to avoid a compiler error in gcc 4.7.1 on SUSE Linux.

Thanks to Volker Härtel for finding this.

dlib/optimization/find_max_parse_cky.h

@@ -259,7 +259,7 @@ namespace dlib
             }
             else
             {
-                if (tree[i].c.begin < words.size())
+                if ((tree[i].c.begin) < words.size())
                 {
                     out << words[tree[i].c.begin] << " ";
                 }