* lisp/emacs-lisp/cl-generic.el: Add support for cl-next-method-p.

* lisp/emacs-lisp/cl-generic.el: Add support for cl-next-method-p.

(cl-defmethod): Add edebug spec.
(cl--generic-build-combined-method): Fix call to
cl-no-applicable-method.
(cl--generic-nnm-sample, cl--generic-cnm-sample): New constant.
(cl--generic-isnot-nnm-p): New function.
(cl--generic-lambda): Use it to add support for cl-next-method-p.
(cl-no-next-method, cl-no-applicable-method): Simplify arg list.
(cl-next-method-p): New function.