Changed test_ranking_function() and cross_validate_ranking_trainer() slightly

to avoid a run time error in gcc 4.7.

dlib/svm/ranking_tools.h

@@ -227,7 +227,7 @@ namespace dlib
                 return true;
             else if (a.first > b.first)
                 return false;
-            else if (a.second == true)
+            else if (a.second && !b.second)
                 return true;
             else
                 return false;

dlib/test/ranking.cpp

@@ -144,6 +144,10 @@ namespace
         samples.push_back(p);
         dlog << LINFO << "cv-accuracy: "<< cross_validate_ranking_trainer(trainer, samples,4);
         DLIB_TEST(equal(cross_validate_ranking_trainer(trainer, samples,4) , res));
+
+        df.basis_vectors(0) = 0;
+        dlog << LINFO << "BAD RANKING:" << test_ranking_function(df, samples);
+        DLIB_TEST(test_ranking_function(df, samples)(1) < 0.5);
     }
 
 // ----------------------------------------------------------------------------------------