* goops.scm (upgrade-generic-with-setter,

* goops.scm (upgrade-generic-with-setter,
compute-new-list-of-methods): Use methods slot directly instead of
generic-function-methods.
(upgrade-generic-with-setter): Handle <extended-generic>:s.
(define-extended-generic): New syntax.
(make-extended-generic): New function.

* goops.c, goops.h (scm_class_extended_generic_with_setter): New
class.
(scm_compute_applicable_methods): Use scm_generic_function_methods.

* goops.c (scm_generic_function_methods): Support extended
generic functions.