Added message to test so that the next time it fails on Appvetor we can

see what happened.

dlib/test/cca.cpp

@@ -126,7 +126,7 @@ namespace
 
             const double trans_error = max(abs(L*Ltrans - R*Rtrans));
             dlog << LINFO << "trans_error: "<< trans_error;
-            DLIB_TEST(trans_error < 1e-9);
+            DLIB_TEST_MSG(trans_error < 1e-9, trans_error);
         }
         {
             correlations = cca(mat_to_sparse(L), mat_to_sparse(R), Ltrans, Rtrans, min(m,n), max(n,n2)+6, 4);