Added a missing requirement and ASSERT.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402954

dlib/svm/kcentroid.h

@@ -165,6 +165,13 @@ namespace dlib
             const kcentroid& x
         ) const
         {
+            // make sure requires clause is not broken
+            DLIB_ASSERT(x.get_kernel() == get_kernel(),
+                "\tscalar_type kcentroid::inner_product(const kcentroid& x)"
+                << "\n\tYou can only compare two kcentroid objects if they use the same kernel"
+                << "\n\tthis: " << this
+                );
+
             scalar_type temp = 0; 
             for (unsigned long i = 0; i < alpha.size(); ++i)
             {

dlib/svm/kcentroid_abstract.h

@@ -180,6 +180,8 @@ namespace dlib
             const kcentroid& x
         ) const;
         /*!
+            requires
+                - x.get_kernel() == get_kernel()
             ensures
                 - returns the inner product between x and this centroid object.
         !*/