EIEIO&cl-generic: Add obsolescence warnings and fix corner case

EIEIO&cl-generic: Add obsolescence warnings and fix corner case

* lisp/emacs-lisp/cl-generic.el (cl-generic-define-method): Correctly handle
introduction of a new dispatch argument.
(cl--generic-cache-miss): Handle dispatch on an argument which was not
considered as dispatchable for this method.
(cl-defmethod): Warn when adding a method to an obsolete generic function.
(cl--generic-lambda): Make sure it works if cl-lib is not yet loaded.

* lisp/emacs-lisp/eieio-generic.el (eieio--defgeneric-init-form):
Use autoloadp.

* lisp/emacs-lisp/eieio.el (defclass): Add obsolescence warning for the
`newname' argument.

* test/automated/cl-generic-tests.el (cl-generic-test-10-weird): New test.
Rename other tests to preserve ordering.