Made this code slightly more robust.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403046

dlib/svm/roc_trainer.h

@@ -5,6 +5,7 @@
 
 #include "roc_trainer_abstract.h"
 #include "../algs.h"
+#include <limits>
 
 namespace dlib
 {
@@ -101,6 +102,16 @@ namespace dlib
 
             df.b = scores[idx];
 
+            // In this case add a very small extra amount to the bias so that all the samples
+            // with the class_selection label are classified correctly.
+            if (desired_accuracy == 1)
+            {
+                if (class_selection == +1)
+                    df.b -= std::numeric_limits<scalar_type>::epsilon()*df.b;
+                else
+                    df.b += std::numeric_limits<scalar_type>::epsilon()*df.b;
+            }
+
             return df;
         }