Now if you don't define it you get a reasonable default behavior
rather than a compiler error.

--HG--
rename : examples/svm_ex.cpp => examples/sequence_labeler_ex.cpp

and cleaned up a few other related things.

labeling using dlib's structural SVM implementation.

to the cross_validate_multiclass_trainer() routine.  Not it will
throw an exception if the number of folds is too big rather than
just producing a confusing result.

by these two objects.

of unsorted sparse vectors.

zero order model had negative factor values.

defined order and num_states parameters.

work right if the column contained a NULL.